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 $42.53   13.503%   $48.2728   $48.27   $48.25   $48.30  
  Purchase #2 $61.97   5.358%   $65.2904   $65.29   $65.30   $65.30  
  Purchase #3 $95.84   8.624%   $104.1052   $104.11   $104.10   $104.10  
  Purchase #4 $122.32   11.819%   $136.777   $136.78   $136.80   $136.80  
  Purchase #5 $217.67   4.347%   $227.1321   $227.13   $227.15   $227.10  
  Purchase #6 $57.65   12.208%   $64.6879   $64.69   $64.70   $64.70  
  Purchase #7 $240.38   7.544%   $258.5143   $258.51   $258.50   $258.50  
  7 purchase totals = $838.36       $904.7797   $904.78   $904.80   $904.80