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 $87.58   12.391%   $98.432   $98.43   $98.45   $98.40  
  Purchase #2 $114.74   8.503%   $124.4963   $124.50   $124.50   $124.50  
  Purchase #3 $167.99   6.238%   $178.4692   $178.47   $178.45   $178.50  
  Purchase #4 $250.51   7.296%   $268.7872   $268.79   $268.80   $268.80  
  Purchase #5 $46.66   10.150%   $51.396   $51.40   $51.40   $51.40  
  Purchase #6 $168.41   3.108%   $173.6442   $173.64   $173.65   $173.60  
  Purchase #7 $76.82   9.220%   $83.9028   $83.90   $83.90   $83.90  
  7 purchase totals = $912.71       $979.1277   $979.13   $979.15   $979.10