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 $203.69   11.232%   $226.5685   $226.57   $226.55   $226.60  
  Purchase #2 $123.90   9.201%   $135.3   $135.30   $135.30   $135.30  
  Purchase #3 $186.70   3.484%   $193.2046   $193.20   $193.20   $193.20  
  Purchase #4 $92.86   7.655%   $99.9684   $99.97   $99.95   $100.00  
  Purchase #5 $93.78   11.181%   $104.2655   $104.27   $104.25   $104.30  
  Purchase #6 $138.28   13.699%   $157.223   $157.22   $157.20   $157.20  
  Purchase #7 $48.62   8.522%   $52.7634   $52.76   $52.75   $52.80  
  7 purchase totals = $887.83       $969.2934   $969.29   $969.20   $969.40