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 $59.73   5.680%   $63.1227   $63.12   $63.10   $63.10  
  Purchase #2 $21.71   5.319%   $22.8648   $22.86   $22.85   $22.90  
  Purchase #3 $221.71   3.646%   $229.7935   $229.79   $229.80   $229.80  
  Purchase #4 $157.98   3.149%   $162.9548   $162.95   $162.95   $163.00  
  Purchase #5 $65.79   8.786%   $71.5703   $71.57   $71.55   $71.60  
  Purchase #6 $155.94   4.503%   $162.962   $162.96   $162.95   $163.00  
  Purchase #7 $138.68   3.741%   $143.868   $143.87   $143.85   $143.90  
  7 purchase totals = $821.54       $857.1361   $857.12   $857.05   $857.30