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	$11.67	5.282%	$12.2864	$12.29	$12.30	$12.30
Purchase #2	$162.77	6.811%	$173.8563	$173.86	$173.85	$173.90
Purchase #3	$169.49	11.567%	$189.0949	$189.09	$189.10	$189.10
Purchase #4	$79.42	11.375%	$88.454	$88.45	$88.45	$88.50
Purchase #5	$140.46	4.863%	$147.2906	$147.29	$147.30	$147.30
Purchase #6	$75.44	3.443%	$78.0374	$78.04	$78.05	$78.00
Purchase #7	$247.65	10.289%	$273.1307	$273.13	$273.15	$273.10
7 purchase totals =	$886.90		$962.1503	$962.15	$962.20	$962.20