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 $62.39   5.725%   $65.9618   $65.96   $65.95   $66.00  
  Purchase #2 $173.93   13.825%   $197.9758   $197.98   $198.00   $198.00  
  Purchase #3 $37.27   7.773%   $40.167   $40.17   $40.15   $40.20  
  Purchase #4 $64.36   13.329%   $72.9385   $72.94   $72.95   $72.90  
  Purchase #5 $33.75   8.601%   $36.6528   $36.65   $36.65   $36.70  
  Purchase #6 $97.82   3.417%   $101.1625   $101.16   $101.15   $101.20  
  Purchase #7 $87.70   4.578%   $91.7149   $91.71   $91.70   $91.70  
  7 purchase totals = $557.22       $606.5733   $606.57   $606.55   $606.70