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 $67.48   12.686%   $76.0405   $76.04   $76.05   $76.00  
  Purchase #2 $124.58   11.619%   $139.055   $139.06   $139.05   $139.10  
  Purchase #3 $236.41   5.634%   $249.7293   $249.73   $249.75   $249.70  
  Purchase #4 $95.67   6.175%   $101.5776   $101.58   $101.60   $101.60  
  Purchase #5 $174.39   11.289%   $194.0769   $194.08   $194.10   $194.10  
  Purchase #6 $61.68   8.565%   $66.9629   $66.96   $66.95   $67.00  
  Purchase #7 $166.43   10.767%   $184.3495   $184.35   $184.35   $184.30  
  7 purchase totals = $926.64       $1,011.7917   $1,011.80   $1,011.85   $1,011.80