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 $58.76   13.710%   $66.816   $66.82   $66.80   $66.80  
  Purchase #2 $109.55   6.465%   $116.6324   $116.63   $116.65   $116.60  
  Purchase #3 $227.47   4.865%   $238.5364   $238.54   $238.55   $238.50  
  Purchase #4 $126.34   7.349%   $135.6247   $135.62   $135.60   $135.60  
  Purchase #5 $176.75   8.412%   $191.6182   $191.62   $191.60   $191.60  
  Purchase #6 $108.57   9.639%   $119.0351   $119.04   $119.05   $119.00  
  Purchase #7 $15.60   3.854%   $16.2012   $16.20   $16.20   $16.20  
  7 purchase totals = $823.04       $884.4640   $884.47   $884.45   $884.30