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 $247.34   11.660%   $276.1798   $276.18   $276.20   $276.20  
  Purchase #2 $212.98   11.105%   $236.6314   $236.63   $236.65   $236.60  
  Purchase #3 $59.45   9.867%   $65.3159   $65.32   $65.30   $65.30  
  Purchase #4 $89.45   13.340%   $101.3826   $101.38   $101.40   $101.40  
  Purchase #5 $137.26   11.256%   $152.71   $152.71   $152.70   $152.70  
  Purchase #6 $201.49   11.644%   $224.9515   $224.95   $224.95   $225.00  
  Purchase #7 $138.80   13.670%   $157.774   $157.77   $157.75   $157.80  
  7 purchase totals = $1,086.77       $1,214.9452   $1,214.94   $1,214.95   $1,215.00