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 $8.87   5.216%   $9.3327   $9.33   $9.35   $9.30  
  Purchase #2 $114.28   3.822%   $118.6478   $118.65   $118.65   $118.60  
  Purchase #3 $88.63   10.508%   $97.9432   $97.94   $97.95   $97.90  
  Purchase #4 $215.62   5.590%   $227.6732   $227.67   $227.65   $227.70  
  Purchase #5 $249.93   10.230%   $275.4978   $275.50   $275.50   $275.50  
  Purchase #6 $84.86   9.124%   $92.6026   $92.60   $92.60   $92.60  
  Purchase #7 $175.53   9.376%   $191.9877   $191.99   $192.00   $192.00  
  7 purchase totals = $937.72       $1,013.6850   $1,013.68   $1,013.70   $1,013.60