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 $214.39   11.355%   $238.734   $238.73   $238.75   $238.70  
  Purchase #2 $48.88   8.857%   $53.2093   $53.21   $53.20   $53.20  
  Purchase #3 $92.81   9.527%   $101.652   $101.65   $101.65   $101.70  
  Purchase #4 $44.54   4.260%   $46.4374   $46.44   $46.45   $46.40  
  Purchase #5 $123.27   9.616%   $135.1236   $135.12   $135.10   $135.10  
  Purchase #6 $87.53   9.534%   $95.8751   $95.88   $95.90   $95.90  
  Purchase #7 $250.75   3.766%   $260.1932   $260.19   $260.20   $260.20  
  7 purchase totals = $862.17       $931.2246   $931.22   $931.25   $931.20