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 $177.66   4.277%   $185.2585   $185.26   $185.25   $185.30  
  Purchase #2 $119.67   5.219%   $125.9156   $125.92   $125.90   $125.90  
  Purchase #3 $243.85   7.117%   $261.2048   $261.20   $261.20   $261.20  
  Purchase #4 $194.93   5.277%   $205.2165   $205.22   $205.20   $205.20  
  Purchase #5 $97.41   4.261%   $101.5606   $101.56   $101.55   $101.60  
  Purchase #6 $154.74   9.144%   $168.8894   $168.89   $168.90   $168.90  
  Purchase #7 $203.41   5.155%   $213.8958   $213.90   $213.90   $213.90  
  7 purchase totals = $1,191.67       $1,261.9412   $1,261.95   $1,261.90   $1,262.00