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 $66.72   10.418%   $73.6709   $73.67   $73.65   $73.70  
  Purchase #2 $46.89   3.411%   $48.4894   $48.49   $48.50   $48.50  
  Purchase #3 $215.70   6.425%   $229.5587   $229.56   $229.55   $229.60  
  Purchase #4 $163.43   5.227%   $171.9725   $171.97   $171.95   $172.00  
  Purchase #5 $206.66   6.261%   $219.599   $219.60   $219.60   $219.60  
  Purchase #6 $65.97   3.161%   $68.0553   $68.06   $68.05   $68.10  
  Purchase #7 $18.46   9.438%   $20.2023   $20.20   $20.20   $20.20  
  7 purchase totals = $783.83       $831.5481   $831.55   $831.50   $831.70