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 $204.86   4.602%   $214.2877   $214.29   $214.30   $214.30  
  Purchase #2 $170.37   7.514%   $183.1716   $183.17   $183.15   $183.20  
  Purchase #3 $127.41   13.863%   $145.0728   $145.07   $145.05   $145.10  
  Purchase #4 $93.91   3.635%   $97.3236   $97.32   $97.30   $97.30  
  Purchase #5 $167.85   3.183%   $173.1927   $173.19   $173.20   $173.20  
  Purchase #6 $107.99   8.269%   $116.9197   $116.92   $116.90   $116.90  
  Purchase #7 $68.94   3.752%   $71.5266   $71.53   $71.55   $71.50  
  7 purchase totals = $941.33       $1,001.4947   $1,001.49   $1,001.45   $1,001.50