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 $43.34   9.267%   $47.3563   $47.36   $47.35   $47.40  
  Purchase #2 $56.38   4.571%   $58.9571   $58.96   $58.95   $59.00  
  Purchase #3 $26.25   9.206%   $28.6666   $28.67   $28.65   $28.70  
  Purchase #4 $182.27   13.341%   $206.5866   $206.59   $206.60   $206.60  
  Purchase #5 $241.28   12.396%   $271.1891   $271.19   $271.20   $271.20  
  Purchase #6 $44.88   6.292%   $47.7038   $47.70   $47.70   $47.70  
  Purchase #7 $244.43   3.671%   $253.403   $253.40   $253.40   $253.40  
  7 purchase totals = $838.83       $913.8625   $913.87   $913.85   $914.00