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	$192.41	10.722%	$213.0402	$213.04	$213.05	$213.00
Purchase #2	$40.33	5.172%	$42.4159	$42.42	$42.40	$42.40
Purchase #3	$118.60	11.622%	$132.3837	$132.38	$132.40	$132.40
Purchase #4	$167.72	10.526%	$185.3742	$185.37	$185.35	$185.40
Purchase #5	$215.96	7.780%	$232.7617	$232.76	$232.75	$232.80
Purchase #6	$62.96	6.246%	$66.8925	$66.89	$66.90	$66.90
Purchase #7	$38.47	11.334%	$42.8302	$42.83	$42.85	$42.80
7 purchase totals =	$836.45		$915.6984	$915.69	$915.70	$915.70