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 $228.44   12.428%   $256.8305   $256.83   $256.85   $256.80  
  Purchase #2 $241.27   5.205%   $253.8281   $253.83   $253.85   $253.80  
  Purchase #3 $235.41   12.579%   $265.0222   $265.02   $265.00   $265.00  
  Purchase #4 $26.73   7.489%   $28.7318   $28.73   $28.75   $28.70  
  Purchase #5 $63.98   4.639%   $66.948   $66.95   $66.95   $66.90  
  Purchase #6 $125.56   10.669%   $138.956   $138.96   $138.95   $139.00  
  Purchase #7 $12.95   12.559%   $14.5764   $14.58   $14.60   $14.60  
  7 purchase totals = $934.34       $1,024.8930   $1,024.90   $1,024.95   $1,024.80