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 $11.45   9.227%   $12.5065   $12.51   $12.50   $12.50  
  Purchase #2 $161.87   3.290%   $167.1955   $167.20   $167.20   $167.20  
  Purchase #3 $67.25   4.163%   $70.0496   $70.05   $70.05   $70.00  
  Purchase #4 $135.49   6.224%   $143.9229   $143.92   $143.90   $143.90  
  Purchase #5 $93.78   11.344%   $104.4184   $104.42   $104.40   $104.40  
  Purchase #6 $237.88   13.215%   $269.3158   $269.32   $269.30   $269.30  
  Purchase #7 $217.79   13.215%   $246.5709   $246.57   $246.55   $246.60  
  7 purchase totals = $925.51       $1,013.9796   $1,013.99   $1,013.90   $1,013.90