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 $195.73   6.597%   $208.6423   $208.64   $208.65   $208.60  
  Purchase #2 $201.93   7.843%   $217.7674   $217.77   $217.75   $217.80  
  Purchase #3 $68.76   9.115%   $75.0275   $75.03   $75.05   $75.00  
  Purchase #4 $71.47   3.776%   $74.1687   $74.17   $74.15   $74.20  
  Purchase #5 $16.96   4.565%   $17.7342   $17.73   $17.75   $17.70  
  Purchase #6 $12.49   8.793%   $13.5882   $13.59   $13.60   $13.60  
  Purchase #7 $42.39   11.175%   $47.1271   $47.13   $47.15   $47.10  
  7 purchase totals = $609.73       $654.0554   $654.06   $654.10   $654.00