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 $197.82   8.858%   $215.3429   $215.34   $215.35   $215.30  
  Purchase #2 $67.89   12.386%   $76.2989   $76.30   $76.30   $76.30  
  Purchase #3 $218.33   12.317%   $245.2217   $245.22   $245.20   $245.20  
  Purchase #4 $215.29   6.649%   $229.6046   $229.60   $229.60   $229.60  
  Purchase #5 $149.38   6.531%   $159.136   $159.14   $159.15   $159.10  
  Purchase #6 $139.43   9.844%   $153.1555   $153.16   $153.15   $153.20  
  Purchase #7 $185.49   3.504%   $191.9896   $191.99   $192.00   $192.00  
  7 purchase totals = $1,173.63       $1,270.7492   $1,270.75   $1,270.75   $1,270.70