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 $231.46   10.781%   $256.4137   $256.41   $256.40   $256.40  
  Purchase #2 $185.35   9.501%   $202.9601   $202.96   $202.95   $203.00  
  Purchase #3 $104.32   13.449%   $118.35   $118.35   $118.35   $118.40  
  Purchase #4 $237.26   9.820%   $260.5589   $260.56   $260.55   $260.60  
  Purchase #5 $226.49   6.311%   $240.7838   $240.78   $240.80   $240.80  
  Purchase #6 $5.34   11.289%   $5.9428   $5.94   $5.95   $5.90  
  Purchase #7 $171.42   6.294%   $182.2092   $182.21   $182.20   $182.20  
  7 purchase totals = $1,161.64       $1,267.2185   $1,267.21   $1,267.20   $1,267.30