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 $206.86   4.532%   $216.2349   $216.23   $216.25   $216.20  
  Purchase #2 $88.35   10.492%   $97.6197   $97.62   $97.60   $97.60  
  Purchase #3 $7.30   8.677%   $7.9334   $7.93   $7.95   $7.90  
  Purchase #4 $42.41   11.532%   $47.3007   $47.30   $47.30   $47.30  
  Purchase #5 $98.60   6.759%   $105.2644   $105.26   $105.25   $105.30  
  Purchase #6 $224.27   10.692%   $248.2489   $248.25   $248.25   $248.20  
  Purchase #7 $119.40   6.164%   $126.7598   $126.76   $126.75   $126.80  
  7 purchase totals = $787.19       $849.3618   $849.35   $849.35   $849.30