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 $116.33   9.140%   $126.9626   $126.96   $126.95   $127.00  
  Purchase #2 $13.30   9.513%   $14.5652   $14.57   $14.55   $14.60  
  Purchase #3 $109.38   6.300%   $116.2709   $116.27   $116.25   $116.30  
  Purchase #4 $108.27   8.469%   $117.4394   $117.44   $117.45   $117.40  
  Purchase #5 $242.62   5.331%   $255.5541   $255.55   $255.55   $255.60  
  Purchase #6 $206.62   8.745%   $224.6889   $224.69   $224.70   $224.70  
  Purchase #7 $115.53   3.218%   $119.2478   $119.25   $119.25   $119.20  
  7 purchase totals = $912.05       $974.7289   $974.73   $974.70   $974.80