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 $228.55   5.550%   $241.2345   $241.23   $241.25   $241.20  
  Purchase #2 $95.92   5.591%   $101.2829   $101.28   $101.30   $101.30  
  Purchase #3 $84.51   3.794%   $87.7163   $87.72   $87.70   $87.70  
  Purchase #4 $75.44   11.347%   $84.0002   $84.00   $84.00   $84.00  
  Purchase #5 $104.73   9.421%   $114.5966   $114.60   $114.60   $114.60  
  Purchase #6 $30.63   7.423%   $32.9037   $32.90   $32.90   $32.90  
  Purchase #7 $91.34   11.741%   $102.0642   $102.06   $102.05   $102.10  
  7 purchase totals = $711.12       $763.7984   $763.79   $763.80   $763.80