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 $73.41   13.373%   $83.2271   $83.23   $83.25   $83.20  
  Purchase #2 $137.67   13.781%   $156.6423   $156.64   $156.65   $156.60  
  Purchase #3 $208.47   4.542%   $217.9387   $217.94   $217.95   $217.90  
  Purchase #4 $241.98   4.772%   $253.5273   $253.53   $253.55   $253.50  
  Purchase #5 $70.99   11.250%   $78.9764   $78.98   $79.00   $79.00  
  Purchase #6 $92.61   12.626%   $104.3029   $104.30   $104.30   $104.30  
  Purchase #7 $142.55   3.858%   $148.0496   $148.05   $148.05   $148.00  
  7 purchase totals = $967.68       $1,042.6643   $1,042.67   $1,042.75   $1,042.50