Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $240.51   11.255%   $267.5794   $267.58   $267.60   $267.60  
  Purchase #2 $159.26   10.106%   $175.3548   $175.35   $175.35   $175.40  
  Purchase #3 $173.33   13.250%   $196.2962   $196.30   $196.30   $196.30  
  Purchase #4 $224.95   13.224%   $254.6974   $254.70   $254.70   $254.70  
  Purchase #5 $170.80   6.867%   $182.5288   $182.53   $182.55   $182.50  
  Purchase #6 $133.45   12.510%   $150.1446   $150.14   $150.15   $150.10  
  Purchase #7 $123.37   13.244%   $139.7091   $139.71   $139.70   $139.70  
  7 purchase totals = $1,225.67       $1,366.3103   $1,366.31   $1,366.35   $1,366.30