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 $183.43   12.859%   $207.0173   $207.02   $207.00   $207.00  
  Purchase #2 $129.92   10.832%   $143.9929   $143.99   $144.00   $144.00  
  Purchase #3 $33.68   3.593%   $34.8901   $34.89   $34.90   $34.90  
  Purchase #4 $168.33   4.109%   $175.2467   $175.25   $175.25   $175.20  
  Purchase #5 $13.92   5.747%   $14.72   $14.72   $14.70   $14.70  
  Purchase #6 $30.61   10.647%   $33.869   $33.87   $33.85   $33.90  
  Purchase #7 $105.55   10.110%   $116.2211   $116.22   $116.20   $116.20  
  7 purchase totals = $665.44       $725.9571   $725.96   $725.90   $725.90