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 $201.57   12.241%   $226.2442   $226.24   $226.25   $226.20  
  Purchase #2 $95.74   3.365%   $98.9617   $98.96   $98.95   $99.00  
  Purchase #3 $52.38   11.472%   $58.389   $58.39   $58.40   $58.40  
  Purchase #4 $215.71   8.265%   $233.5384   $233.54   $233.55   $233.50  
  Purchase #5 $205.27   10.718%   $227.2708   $227.27   $227.25   $227.30  
  Purchase #6 $25.69   11.114%   $28.5452   $28.55   $28.55   $28.50  
  Purchase #7 $177.81   12.223%   $199.5437   $199.54   $199.55   $199.50  
  7 purchase totals = $974.17       $1,072.4930   $1,072.49   $1,072.50   $1,072.40