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 $71.35   3.636%   $73.9443   $73.94   $73.95   $73.90  
  Purchase #2 $211.95   7.351%   $227.5304   $227.53   $227.55   $227.50  
  Purchase #3 $237.91   9.779%   $261.1752   $261.18   $261.20   $261.20  
  Purchase #4 $224.56   5.202%   $236.2416   $236.24   $236.25   $236.20  
  Purchase #5 $93.67   4.433%   $97.8224   $97.82   $97.80   $97.80  
  Purchase #6 $157.83   4.252%   $164.5409   $164.54   $164.55   $164.50  
  Purchase #7 $231.91   4.463%   $242.2601   $242.26   $242.25   $242.30  
  7 purchase totals = $1,229.18       $1,303.5149   $1,303.51   $1,303.55   $1,303.40