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 $48.63   11.865%   $54.3999   $54.40   $54.40   $54.40  
  Purchase #2 $190.36   8.202%   $205.9733   $205.97   $205.95   $206.00  
  Purchase #3 $207.68   12.651%   $233.9536   $233.95   $233.95   $234.00  
  Purchase #4 $180.95   10.567%   $200.071   $200.07   $200.05   $200.10  
  Purchase #5 $44.47   12.863%   $50.1902   $50.19   $50.20   $50.20  
  Purchase #6 $213.73   9.545%   $234.1305   $234.13   $234.15   $234.10  
  Purchase #7 $224.28   8.441%   $243.2115   $243.21   $243.20   $243.20  
  7 purchase totals = $1,110.10       $1,221.9300   $1,221.92   $1,221.90   $1,222.00