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 $228.69   3.624%   $236.9777   $236.98   $237.00   $237.00  
  Purchase #2 $209.25   9.447%   $229.0178   $229.02   $229.00   $229.00  
  Purchase #3 $129.86   8.631%   $141.0682   $141.07   $141.05   $141.10  
  Purchase #4 $52.75   5.288%   $55.5394   $55.54   $55.55   $55.50  
  Purchase #5 $236.99   12.848%   $267.4385   $267.44   $267.45   $267.40  
  Purchase #6 $215.86   12.497%   $242.836   $242.84   $242.85   $242.80  
  Purchase #7 $69.61   10.443%   $76.8794   $76.88   $76.90   $76.90  
  7 purchase totals = $1,143.01       $1,249.7570   $1,249.77   $1,249.80   $1,249.70