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	$84.70	7.174%	$90.7764	$90.78	$90.80	$90.80
Purchase #2	$32.46	5.181%	$34.1418	$34.14	$34.15	$34.10
Purchase #3	$247.41	6.163%	$262.6579	$262.66	$262.65	$262.70
Purchase #4	$123.89	11.297%	$137.8859	$137.89	$137.90	$137.90
Purchase #5	$205.92	3.661%	$213.4587	$213.46	$213.45	$213.50
Purchase #6	$213.78	9.433%	$233.9459	$233.95	$233.95	$233.90
Purchase #7	$158.35	4.851%	$166.0316	$166.03	$166.05	$166.00
7 purchase totals =	$1,066.51		$1,138.8982	$1,138.91	$1,138.95	$1,138.90