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 $88.95   10.541%   $98.3262   $98.33   $98.35   $98.30  
  Purchase #2 $245.54   12.296%   $275.7316   $275.73   $275.75   $275.70  
  Purchase #3 $71.31   6.674%   $76.0692   $76.07   $76.05   $76.10  
  Purchase #4 $190.49   6.177%   $202.2566   $202.26   $202.25   $202.30  
  Purchase #5 $117.38   8.361%   $127.1941   $127.19   $127.20   $127.20  
  Purchase #6 $245.76   9.126%   $268.1881   $268.19   $268.20   $268.20  
  Purchase #7 $203.50   5.358%   $214.4035   $214.40   $214.40   $214.40  
  7 purchase totals = $1,162.93       $1,262.1693   $1,262.17   $1,262.20   $1,262.20