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 $113.56   4.405%   $118.5623   $118.56   $118.55   $118.60  
  Purchase #2 $221.71   8.207%   $239.9057   $239.91   $239.90   $239.90  
  Purchase #3 $123.61   11.513%   $137.8412   $137.84   $137.85   $137.80  
  Purchase #4 $191.69   9.234%   $209.3907   $209.39   $209.40   $209.40  
  Purchase #5 $205.38   3.723%   $213.0263   $213.03   $213.05   $213.00  
  Purchase #6 $243.97   13.271%   $276.3473   $276.35   $276.35   $276.30  
  Purchase #7 $241.91   11.872%   $270.6296   $270.63   $270.65   $270.60  
  7 purchase totals = $1,341.83       $1,465.7031   $1,465.71   $1,465.75   $1,465.60