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 $247.97   5.812%   $262.382   $262.38   $262.40   $262.40  
  Purchase #2 $21.56   3.339%   $22.2799   $22.28   $22.30   $22.30  
  Purchase #3 $35.99   5.561%   $37.9914   $37.99   $38.00   $38.00  
  Purchase #4 $217.34   3.546%   $225.0469   $225.05   $225.05   $225.00  
  Purchase #5 $83.84   7.583%   $90.1976   $90.20   $90.20   $90.20  
  Purchase #6 $63.89   10.188%   $70.3991   $70.40   $70.40   $70.40  
  Purchase #7 $91.35   6.505%   $97.2923   $97.29   $97.30   $97.30  
  7 purchase totals = $761.94       $805.5892   $805.59   $805.65   $805.60