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	$238.42	5.233%	$250.8965	$250.90	$250.90	$250.90
Purchase #2	$158.48	7.674%	$170.6418	$170.64	$170.65	$170.60
Purchase #3	$232.73	3.335%	$240.4915	$240.49	$240.50	$240.50
Purchase #4	$138.82	10.136%	$152.8908	$152.89	$152.90	$152.90
Purchase #5	$135.52	11.799%	$151.51	$151.51	$151.50	$151.50
Purchase #6	$47.29	13.522%	$53.6846	$53.68	$53.70	$53.70
Purchase #7	$9.81	10.735%	$10.8631	$10.86	$10.85	$10.90
7 purchase totals =	$961.07		$1,030.9783	$1,030.97	$1,031.00	$1,031.00