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 $71.47   7.271%   $76.6666   $76.67   $76.65   $76.70  
  Purchase #2 $35.41   13.146%   $40.065   $40.07   $40.05   $40.10  
  Purchase #3 $27.95   11.308%   $31.1106   $31.11   $31.10   $31.10  
  Purchase #4 $146.86   7.262%   $157.525   $157.53   $157.55   $157.50  
  Purchase #5 $182.62   11.647%   $203.8898   $203.89   $203.90   $203.90  
  Purchase #6 $112.78   10.799%   $124.9591   $124.96   $124.95   $125.00  
  Purchase #7 $109.75   4.689%   $114.8962   $114.90   $114.90   $114.90  
  7 purchase totals = $686.84       $749.1123   $749.13   $749.10   $749.20