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	$48.77	3.104%	$50.2838	$50.28	$50.30	$50.30
Purchase #2	$30.98	13.533%	$35.1725	$35.17	$35.15	$35.20
Purchase #3	$121.55	12.801%	$137.1096	$137.11	$137.10	$137.10
Purchase #4	$193.89	13.267%	$219.6134	$219.61	$219.60	$219.60
Purchase #5	$13.54	10.415%	$14.9502	$14.95	$14.95	$15.00
Purchase #6	$102.38	6.780%	$109.3214	$109.32	$109.30	$109.30
Purchase #7	$74.93	4.458%	$78.2704	$78.27	$78.25	$78.30
7 purchase totals =	$586.04		$644.7213	$644.71	$644.65	$644.80