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 $104.98   6.872%   $112.1942   $112.19   $112.20   $112.20  
  Purchase #2 $146.58   3.174%   $151.2324   $151.23   $151.25   $151.20  
  Purchase #3 $149.51   4.853%   $156.7657   $156.77   $156.75   $156.80  
  Purchase #4 $194.71   6.174%   $206.7314   $206.73   $206.75   $206.70  
  Purchase #5 $177.67   10.271%   $195.9185   $195.92   $195.90   $195.90  
  Purchase #6 $122.58   3.800%   $127.238   $127.24   $127.25   $127.20  
  Purchase #7 $249.99   7.536%   $268.8292   $268.83   $268.85   $268.80  
  7 purchase totals = $1,146.02       $1,218.9094   $1,218.91   $1,218.95   $1,218.80