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 $244.29   5.869%   $258.6274   $258.63   $258.65   $258.60  
  Purchase #2 $159.31   4.194%   $165.9915   $165.99   $166.00   $166.00  
  Purchase #3 $55.66   7.392%   $59.7744   $59.77   $59.75   $59.80  
  Purchase #4 $33.56   7.651%   $36.1277   $36.13   $36.15   $36.10  
  Purchase #5 $75.79   4.476%   $79.1824   $79.18   $79.20   $79.20  
  Purchase #6 $174.92   10.317%   $192.9665   $192.97   $192.95   $193.00  
  Purchase #7 $34.76   5.312%   $36.6065   $36.61   $36.60   $36.60  
  7 purchase totals = $778.29       $829.2764   $829.28   $829.30   $829.30