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 $245.63   11.673%   $274.3024   $274.30   $274.30   $274.30  
  Purchase #2 $233.93   5.589%   $247.0043   $247.00   $247.00   $247.00  
  Purchase #3 $82.68   13.583%   $93.9104   $93.91   $93.90   $93.90  
  Purchase #4 $24.38   8.196%   $26.3782   $26.38   $26.40   $26.40  
  Purchase #5 $147.77   5.798%   $156.3377   $156.34   $156.35   $156.30  
  Purchase #6 $104.35   7.790%   $112.4789   $112.48   $112.50   $112.50  
  Purchase #7 $112.79   9.324%   $123.3065   $123.31   $123.30   $123.30  
  7 purchase totals = $951.53       $1,033.7184   $1,033.72   $1,033.75   $1,033.70