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 $236.41   13.120%   $267.427   $267.43   $267.45   $267.40  
  Purchase #2 $215.61   10.342%   $237.9084   $237.91   $237.90   $237.90  
  Purchase #3 $230.78   4.601%   $241.3982   $241.40   $241.40   $241.40  
  Purchase #4 $19.86   6.207%   $21.0927   $21.09   $21.10   $21.10  
  Purchase #5 $192.47   11.585%   $214.7676   $214.77   $214.75   $214.80  
  Purchase #6 $150.41   5.135%   $158.1336   $158.13   $158.15   $158.10  
  Purchase #7 $118.63   9.112%   $129.4396   $129.44   $129.45   $129.40  
  7 purchase totals = $1,164.17       $1,270.1671   $1,270.17   $1,270.20   $1,270.10