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 $243.59   7.443%   $261.7204   $261.72   $261.70   $261.70  
  Purchase #2 $69.68   13.180%   $78.8638   $78.86   $78.85   $78.90  
  Purchase #3 $249.55   8.185%   $269.9757   $269.98   $270.00   $270.00  
  Purchase #4 $202.46   6.556%   $215.7333   $215.73   $215.75   $215.70  
  Purchase #5 $60.63   5.767%   $64.1265   $64.13   $64.15   $64.10  
  Purchase #6 $102.94   7.609%   $110.7727   $110.77   $110.75   $110.80  
  Purchase #7 $41.29   12.486%   $46.4455   $46.45   $46.45   $46.40  
  7 purchase totals = $970.14       $1,047.6379   $1,047.64   $1,047.65   $1,047.60