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 $247.36   10.266%   $272.754   $272.75   $272.75   $272.80  
  Purchase #2 $48.58   5.804%   $51.3996   $51.40   $51.40   $51.40  
  Purchase #3 $168.36   9.219%   $183.8811   $183.88   $183.90   $183.90  
  Purchase #4 $180.55   6.383%   $192.0745   $192.07   $192.05   $192.10  
  Purchase #5 $44.29   3.719%   $45.9371   $45.94   $45.95   $45.90  
  Purchase #6 $209.57   8.274%   $226.9098   $226.91   $226.90   $226.90  
  Purchase #7 $34.71   4.808%   $36.3789   $36.38   $36.40   $36.40  
  7 purchase totals = $933.42       $1,009.3350   $1,009.33   $1,009.35   $1,009.40