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 $185.46   13.328%   $210.1781   $210.18   $210.20   $210.20  
  Purchase #2 $29.66   3.362%   $30.6572   $30.66   $30.65   $30.70  
  Purchase #3 $94.38   4.154%   $98.3005   $98.30   $98.30   $98.30  
  Purchase #4 $66.34   8.271%   $71.827   $71.83   $71.85   $71.80  
  Purchase #5 $53.77   8.863%   $58.5356   $58.54   $58.55   $58.50  
  Purchase #6 $101.39   8.658%   $110.1683   $110.17   $110.15   $110.20  
  Purchase #7 $205.90   8.131%   $222.6417   $222.64   $222.65   $222.60  
  7 purchase totals = $736.90       $802.3084   $802.32   $802.35   $802.30