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	$110.35	6.261%	$117.259	$117.26	$117.25	$117.30
Purchase #2	$31.29	10.107%	$34.4525	$34.45	$34.45	$34.50
Purchase #3	$174.38	12.838%	$196.7669	$196.77	$196.75	$196.80
Purchase #4	$12.50	7.717%	$13.4646	$13.46	$13.45	$13.50
Purchase #5	$247.31	12.856%	$279.1042	$279.10	$279.10	$279.10
Purchase #6	$17.27	12.842%	$19.4878	$19.49	$19.50	$19.50
Purchase #7	$55.51	3.726%	$57.5783	$57.58	$57.60	$57.60
7 purchase totals =	$648.61		$718.1133	$718.11	$718.10	$718.30