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 $208.40   8.455%   $226.0202   $226.02   $226.00   $226.00  
  Purchase #2 $49.99   8.278%   $54.1282   $54.13   $54.15   $54.10  
  Purchase #3 $151.84   5.106%   $159.593   $159.59   $159.60   $159.60  
  Purchase #4 $46.77   13.334%   $53.0063   $53.01   $53.00   $53.00  
  Purchase #5 $35.41   7.166%   $37.9475   $37.95   $37.95   $37.90  
  Purchase #6 $66.54   9.192%   $72.6564   $72.66   $72.65   $72.70  
  Purchase #7 $193.26   11.617%   $215.711   $215.71   $215.70   $215.70  
  7 purchase totals = $752.21       $819.0626   $819.07   $819.05   $819.00