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	$116.91	13.123%	$132.2521	$132.25	$132.25	$132.30
Purchase #2	$179.36	8.504%	$194.6128	$194.61	$194.60	$194.60
Purchase #3	$53.27	3.429%	$55.0966	$55.10	$55.10	$55.10
Purchase #4	$144.46	6.716%	$154.1619	$154.16	$154.15	$154.20
Purchase #5	$155.95	5.428%	$164.415	$164.42	$164.40	$164.40
Purchase #6	$34.69	7.728%	$37.3708	$37.37	$37.35	$37.40
Purchase #7	$50.94	10.689%	$56.385	$56.39	$56.40	$56.40
7 purchase totals =	$735.58		$794.2942	$794.30	$794.25	$794.40