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 $206.26   10.231%   $227.3625   $227.36   $227.35   $227.40  
  Purchase #2 $221.93   8.327%   $240.4101   $240.41   $240.40   $240.40  
  Purchase #3 $214.73   9.845%   $235.8702   $235.87   $235.85   $235.90  
  Purchase #4 $223.99   5.445%   $236.1863   $236.19   $236.20   $236.20  
  Purchase #5 $150.80   5.772%   $159.5042   $159.50   $159.50   $159.50  
  Purchase #6 $174.63   9.482%   $191.1884   $191.19   $191.20   $191.20  
  Purchase #7 $226.71   4.423%   $236.7374   $236.74   $236.75   $236.70  
  7 purchase totals = $1,419.05       $1,527.2591   $1,527.26   $1,527.25   $1,527.30