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 $24.87   5.462%   $26.2284   $26.23   $26.25   $26.20  
  Purchase #2 $11.88   13.708%   $13.5085   $13.51   $13.50   $13.50  
  Purchase #3 $224.77   8.647%   $244.2059   $244.21   $244.20   $244.20  
  Purchase #4 $26.86   5.599%   $28.3639   $28.36   $28.35   $28.40  
  Purchase #5 $238.43   13.386%   $270.3462   $270.35   $270.35   $270.30  
  Purchase #6 $119.62   7.120%   $128.1369   $128.14   $128.15   $128.10  
  Purchase #7 $48.78   11.209%   $54.2478   $54.25   $54.25   $54.20  
  7 purchase totals = $695.21       $765.0376   $765.05   $765.05   $764.90