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 $62.95   8.630%   $68.3826   $68.38   $68.40   $68.40  
  Purchase #2 $191.26   12.385%   $214.9476   $214.95   $214.95   $214.90  
  Purchase #3 $84.73   6.433%   $90.1807   $90.18   $90.20   $90.20  
  Purchase #4 $51.34   10.758%   $56.8632   $56.86   $56.85   $56.90  
  Purchase #5 $225.70   11.450%   $251.5427   $251.54   $251.55   $251.50  
  Purchase #6 $99.27   5.138%   $104.3705   $104.37   $104.35   $104.40  
  Purchase #7 $60.26   7.286%   $64.6505   $64.65   $64.65   $64.70  
  7 purchase totals = $775.51       $850.9378   $850.93   $850.95   $851.00