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 $146.26   8.132%   $158.1539   $158.15   $158.15   $158.20  
  Purchase #2 $92.36   3.695%   $95.7727   $95.77   $95.75   $95.80  
  Purchase #3 $27.29   13.635%   $31.011   $31.01   $31.00   $31.00  
  Purchase #4 $199.96   7.561%   $215.079   $215.08   $215.10   $215.10  
  Purchase #5 $125.27   13.762%   $142.5097   $142.51   $142.50   $142.50  
  Purchase #6 $249.98   4.746%   $261.8441   $261.84   $261.85   $261.80  
  Purchase #7 $210.53   11.608%   $234.9683   $234.97   $234.95   $235.00  
  7 purchase totals = $1,051.65       $1,139.3387   $1,139.33   $1,139.30   $1,139.40