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 $196.39   11.596%   $219.1634   $219.16   $219.15   $219.20  
  Purchase #2 $155.26   9.318%   $169.7271   $169.73   $169.75   $169.70  
  Purchase #3 $89.59   9.315%   $97.9353   $97.94   $97.95   $97.90  
  Purchase #4 $244.38   13.579%   $277.5644   $277.56   $277.55   $277.60  
  Purchase #5 $54.89   4.307%   $57.2541   $57.25   $57.25   $57.30  
  Purchase #6 $53.55   7.595%   $57.6171   $57.62   $57.60   $57.60  
  Purchase #7 $33.86   5.195%   $35.619   $35.62   $35.60   $35.60  
  7 purchase totals = $827.92       $914.8804   $914.88   $914.85   $914.90