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 $211.49   13.362%   $239.7493   $239.75   $239.75   $239.70  
  Purchase #2 $250.90   4.660%   $262.5919   $262.59   $262.60   $262.60  
  Purchase #3 $216.53   9.687%   $237.5053   $237.51   $237.50   $237.50  
  Purchase #4 $99.94   4.758%   $104.6951   $104.70   $104.70   $104.70  
  Purchase #5 $99.94   4.758%   $104.6951   $104.70   $104.70   $104.70  
  Purchase #6 $189.33   11.430%   $210.9704   $210.97   $210.95   $211.00  
  Purchase #7 $82.89   13.589%   $94.1539   $94.15   $94.15   $94.20  
  7 purchase totals = $1,151.02       $1,254.3610   $1,254.37   $1,254.35   $1,254.40