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	$13.73	11.835%	$15.3549	$15.35	$15.35	$15.40
Purchase #2	$214.90	3.403%	$222.213	$222.21	$222.20	$222.20
Purchase #3	$10.31	9.695%	$11.3096	$11.31	$11.30	$11.30
Purchase #4	$64.92	11.668%	$72.4949	$72.49	$72.50	$72.50
Purchase #5	$208.54	10.823%	$231.1103	$231.11	$231.10	$231.10
Purchase #6	$210.26	13.469%	$238.5799	$238.58	$238.60	$238.60
Purchase #7	$57.66	4.857%	$60.4605	$60.46	$60.45	$60.50
7 purchase totals =	$780.32		$851.5231	$851.51	$851.50	$851.60