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	$140.57	12.309%	$157.8728	$157.87	$157.85	$157.90
Purchase #2	$129.28	12.103%	$144.9268	$144.93	$144.95	$144.90
Purchase #3	$58.94	13.493%	$66.8928	$66.89	$66.90	$66.90
Purchase #4	$75.29	4.185%	$78.4409	$78.44	$78.45	$78.40
Purchase #5	$90.86	11.510%	$101.318	$101.32	$101.30	$101.30
Purchase #6	$15.78	13.191%	$17.8615	$17.86	$17.85	$17.90
Purchase #7	$8.32	13.479%	$9.4415	$9.44	$9.45	$9.40
7 purchase totals =	$519.04		$576.7543	$576.75	$576.75	$576.70