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 $111.70   11.340%   $124.3668   $124.37   $124.35   $124.40  
  Purchase #2 $217.79   10.606%   $240.8888   $240.89   $240.90   $240.90  
  Purchase #3 $95.86   5.522%   $101.1534   $101.15   $101.15   $101.20  
  Purchase #4 $168.40   5.196%   $177.1501   $177.15   $177.15   $177.20  
  Purchase #5 $206.98   13.421%   $234.7588   $234.76   $234.75   $234.80  
  Purchase #6 $135.66   11.491%   $151.2487   $151.25   $151.25   $151.20  
  Purchase #7 $156.95   8.712%   $170.6235   $170.62   $170.60   $170.60  
  7 purchase totals = $1,093.34       $1,200.1901   $1,200.19   $1,200.15   $1,200.30