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 $63.54   8.328%   $68.8316   $68.83   $68.85   $68.80  
  Purchase #2 $210.99   10.487%   $233.1165   $233.12   $233.10   $233.10  
  Purchase #3 $101.36   10.874%   $112.3819   $112.38   $112.40   $112.40  
  Purchase #4 $116.35   13.401%   $131.9421   $131.94   $131.95   $131.90  
  Purchase #5 $98.99   11.619%   $110.4916   $110.49   $110.50   $110.50  
  Purchase #6 $71.42   5.506%   $75.3524   $75.35   $75.35   $75.40  
  Purchase #7 $56.73   9.261%   $61.9838   $61.98   $62.00   $62.00  
  7 purchase totals = $719.38       $794.0999   $794.09   $794.15   $794.10