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 $91.97   4.329%   $95.9514   $95.95   $95.95   $96.00  
  Purchase #2 $17.25   6.856%   $18.4327   $18.43   $18.45   $18.40  
  Purchase #3 $71.33   3.278%   $73.6682   $73.67   $73.65   $73.70  
  Purchase #4 $244.69   13.164%   $276.901   $276.90   $276.90   $276.90  
  Purchase #5 $85.85   8.267%   $92.9472   $92.95   $92.95   $92.90  
  Purchase #6 $202.77   8.451%   $219.9061   $219.91   $219.90   $219.90  
  Purchase #7 $48.40   11.788%   $54.1054   $54.11   $54.10   $54.10  
  7 purchase totals = $762.26       $831.9120   $831.92   $831.90   $831.90