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 $83.72   12.187%   $93.923   $93.92   $93.90   $93.90  
  Purchase #2 $82.47   4.666%   $86.3181   $86.32   $86.30   $86.30  
  Purchase #3 $223.48   5.671%   $236.1536   $236.15   $236.15   $236.20  
  Purchase #4 $72.82   5.677%   $76.954   $76.95   $76.95   $77.00  
  Purchase #5 $112.40   4.528%   $117.4895   $117.49   $117.50   $117.50  
  Purchase #6 $178.89   6.743%   $190.9526   $190.95   $190.95   $191.00  
  Purchase #7 $117.27   12.735%   $132.2043   $132.20   $132.20   $132.20  
  7 purchase totals = $871.05       $933.9951   $933.98   $933.95   $934.10