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 $200.48   6.243%   $212.996   $213.00   $213.00   $213.00  
  Purchase #2 $92.39   6.780%   $98.654   $98.65   $98.65   $98.70  
  Purchase #3 $215.74   12.468%   $242.6385   $242.64   $242.65   $242.60  
  Purchase #4 $65.31   5.258%   $68.744   $68.74   $68.75   $68.70  
  Purchase #5 $193.50   8.801%   $210.5299   $210.53   $210.55   $210.50  
  Purchase #6 $108.30   8.301%   $117.29   $117.29   $117.30   $117.30  
  Purchase #7 $46.91   4.596%   $49.066   $49.07   $49.05   $49.10  
  7 purchase totals = $922.63       $999.9184   $999.92   $999.95   $999.90