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 $194.97   10.393%   $215.2332   $215.23   $215.25   $215.20  
  Purchase #2 $239.95   12.105%   $268.9959   $269.00   $269.00   $269.00  
  Purchase #3 $121.58   3.626%   $125.9885   $125.99   $126.00   $126.00  
  Purchase #4 $157.51   4.654%   $164.8405   $164.84   $164.85   $164.80  
  Purchase #5 $240.45   12.279%   $269.9749   $269.97   $269.95   $270.00  
  Purchase #6 $26.53   3.396%   $27.431   $27.43   $27.45   $27.40  
  Purchase #7 $243.45   13.269%   $275.7534   $275.75   $275.75   $275.80  
  7 purchase totals = $1,224.44       $1,348.2174   $1,348.21   $1,348.25   $1,348.20