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 $236.44   10.733%   $261.8171   $261.82   $261.80   $261.80  
  Purchase #2 $136.55   3.510%   $141.3429   $141.34   $141.35   $141.30  
  Purchase #3 $180.29   3.709%   $186.977   $186.98   $187.00   $187.00  
  Purchase #4 $155.60   6.312%   $165.4215   $165.42   $165.40   $165.40  
  Purchase #5 $249.88   9.136%   $272.709   $272.71   $272.70   $272.70  
  Purchase #6 $221.95   11.281%   $246.9882   $246.99   $247.00   $247.00  
  Purchase #7 $132.36   6.495%   $140.9568   $140.96   $140.95   $141.00  
  7 purchase totals = $1,313.07       $1,416.2125   $1,416.22   $1,416.20   $1,416.20