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 $92.49   6.202%   $98.2262   $98.23   $98.25   $98.20  
  Purchase #2 $111.42   8.840%   $121.2695   $121.27   $121.25   $121.30  
  Purchase #3 $102.26   13.502%   $116.0671   $116.07   $116.05   $116.10  
  Purchase #4 $196.81   9.570%   $215.6447   $215.64   $215.65   $215.60  
  Purchase #5 $115.48   3.395%   $119.4005   $119.40   $119.40   $119.40  
  Purchase #6 $16.35   13.507%   $18.5584   $18.56   $18.55   $18.60  
  Purchase #7 $94.73   13.463%   $107.4835   $107.48   $107.50   $107.50  
  7 purchase totals = $729.54       $796.6499   $796.65   $796.65   $796.70