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 $60.51   6.342%   $64.3475   $64.35   $64.35   $64.30  
  Purchase #2 $167.99   10.393%   $185.4492   $185.45   $185.45   $185.40  
  Purchase #3 $153.32   6.375%   $163.0942   $163.09   $163.10   $163.10  
  Purchase #4 $108.77   5.128%   $114.3477   $114.35   $114.35   $114.30  
  Purchase #5 $247.40   10.569%   $273.5477   $273.55   $273.55   $273.50  
  Purchase #6 $194.68   13.618%   $221.1915   $221.19   $221.20   $221.20  
  Purchase #7 $54.33   7.667%   $58.4955   $58.50   $58.50   $58.50  
  7 purchase totals = $987.00       $1,080.4733   $1,080.48   $1,080.50   $1,080.30