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 $61.74   8.602%   $67.0509   $67.05   $67.05   $67.10  
  Purchase #2 $86.34   5.852%   $91.3926   $91.39   $91.40   $91.40  
  Purchase #3 $147.90   3.436%   $152.9818   $152.98   $153.00   $153.00  
  Purchase #4 $57.26   5.246%   $60.2639   $60.26   $60.25   $60.30  
  Purchase #5 $52.78   10.105%   $58.1134   $58.11   $58.10   $58.10  
  Purchase #6 $132.95   11.498%   $148.2366   $148.24   $148.25   $148.20  
  Purchase #7 $222.99   10.862%   $247.2112   $247.21   $247.20   $247.20  
  7 purchase totals = $761.96       $825.2504   $825.24   $825.25   $825.30