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 $73.34   12.687%   $82.6446   $82.64   $82.65   $82.60  
  Purchase #2 $63.32   7.272%   $67.9246   $67.92   $67.90   $67.90  
  Purchase #3 $142.71   9.845%   $156.7598   $156.76   $156.75   $156.80  
  Purchase #4 $244.93   8.631%   $266.0699   $266.07   $266.05   $266.10  
  Purchase #5 $148.86   5.465%   $156.9952   $157.00   $157.00   $157.00  
  Purchase #6 $171.45   6.174%   $182.0353   $182.04   $182.05   $182.00  
  Purchase #7 $114.64   4.761%   $120.098   $120.10   $120.10   $120.10  
  7 purchase totals = $959.25       $1,032.5274   $1,032.53   $1,032.50   $1,032.50