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 $169.27   13.638%   $192.355   $192.36   $192.35   $192.40  
  Purchase #2 $63.82   7.185%   $68.4055   $68.41   $68.40   $68.40  
  Purchase #3 $237.62   5.376%   $250.3945   $250.39   $250.40   $250.40  
  Purchase #4 $205.27   13.392%   $232.7598   $232.76   $232.75   $232.80  
  Purchase #5 $248.68   6.618%   $265.1376   $265.14   $265.15   $265.10  
  Purchase #6 $119.96   8.600%   $130.2766   $130.28   $130.30   $130.30  
  Purchase #7 $188.61   13.785%   $214.6099   $214.61   $214.60   $214.60  
  7 purchase totals = $1,233.23       $1,353.9389   $1,353.95   $1,353.95   $1,354.00