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 $50.76   13.476%   $57.6004   $57.60   $57.60   $57.60  
  Purchase #2 $232.82   8.147%   $251.7878   $251.79   $251.80   $251.80  
  Purchase #3 $61.49   4.491%   $64.2515   $64.25   $64.25   $64.30  
  Purchase #4 $87.41   11.866%   $97.7821   $97.78   $97.80   $97.80  
  Purchase #5 $31.50   6.734%   $33.6212   $33.62   $33.60   $33.60  
  Purchase #6 $228.34   7.113%   $244.5818   $244.58   $244.60   $244.60  
  Purchase #7 $200.74   13.518%   $227.876   $227.88   $227.90   $227.90  
  7 purchase totals = $893.06       $977.5008   $977.50   $977.55   $977.60