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 $229.61   13.562%   $260.7497   $260.75   $260.75   $260.70  
  Purchase #2 $210.85   10.281%   $232.5275   $232.53   $232.55   $232.50  
  Purchase #3 $32.44   10.516%   $35.8514   $35.85   $35.85   $35.90  
  Purchase #4 $136.73   10.318%   $150.8378   $150.84   $150.85   $150.80  
  Purchase #5 $229.75   13.334%   $260.3849   $260.38   $260.40   $260.40  
  Purchase #6 $141.85   9.534%   $155.374   $155.37   $155.35   $155.40  
  Purchase #7 $84.73   7.115%   $90.7585   $90.76   $90.75   $90.80  
  7 purchase totals = $1,065.96       $1,186.4838   $1,186.48   $1,186.50   $1,186.50