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 $63.46   12.792%   $71.5778   $71.58   $71.60   $71.60  
  Purchase #2 $136.63   12.443%   $153.6309   $153.63   $153.65   $153.60  
  Purchase #3 $96.38   8.678%   $104.7439   $104.74   $104.75   $104.70  
  Purchase #4 $174.34   5.385%   $183.7282   $183.73   $183.75   $183.70  
  Purchase #5 $229.82   6.363%   $244.4434   $244.44   $244.45   $244.40  
  Purchase #6 $107.39   3.194%   $110.82   $110.82   $110.80   $110.80  
  Purchase #7 $47.50   13.643%   $53.9804   $53.98   $54.00   $54.00  
  7 purchase totals = $855.52       $922.9246   $922.92   $923.00   $922.80