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 $242.86   8.436%   $263.3477   $263.35   $263.35   $263.30  
  Purchase #2 $203.60   13.771%   $231.6378   $231.64   $231.65   $231.60  
  Purchase #3 $242.28   9.506%   $265.3111   $265.31   $265.30   $265.30  
  Purchase #4 $224.98   12.713%   $253.5817   $253.58   $253.60   $253.60  
  Purchase #5 $35.40   6.479%   $37.6936   $37.69   $37.70   $37.70  
  Purchase #6 $126.47   10.432%   $139.6634   $139.66   $139.65   $139.70  
  Purchase #7 $76.26   9.128%   $83.221   $83.22   $83.20   $83.20  
  7 purchase totals = $1,151.85       $1,274.4563   $1,274.45   $1,274.45   $1,274.40