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 $59.94   8.474%   $65.0193   $65.02   $65.00   $65.00  
  Purchase #2 $105.83   7.393%   $113.654   $113.65   $113.65   $113.70  
  Purchase #3 $20.34   13.800%   $23.1469   $23.15   $23.15   $23.10  
  Purchase #4 $10.40   4.686%   $10.8873   $10.89   $10.90   $10.90  
  Purchase #5 $173.43   8.862%   $188.7994   $188.80   $188.80   $188.80  
  Purchase #6 $208.42   7.732%   $224.535   $224.54   $224.55   $224.50  
  Purchase #7 $149.75   13.636%   $170.1699   $170.17   $170.15   $170.20  
  7 purchase totals = $728.11       $796.2118   $796.22   $796.20   $796.20