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 $92.44   7.733%   $99.5884   $99.59   $99.60   $99.60  
  Purchase #2 $197.77   7.163%   $211.9363   $211.94   $211.95   $211.90  
  Purchase #3 $44.44   3.427%   $45.963   $45.96   $45.95   $46.00  
  Purchase #4 $242.25   4.266%   $252.5844   $252.58   $252.60   $252.60  
  Purchase #5 $237.43   8.669%   $258.0128   $258.01   $258.00   $258.00  
  Purchase #6 $84.99   4.803%   $89.0721   $89.07   $89.05   $89.10  
  Purchase #7 $143.82   10.181%   $158.4623   $158.46   $158.45   $158.50  
  7 purchase totals = $1,043.14       $1,115.6193   $1,115.61   $1,115.60   $1,115.70