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	$74.66	4.162%	$77.7673	$77.77	$77.75	$77.80
Purchase #2	$163.52	9.834%	$179.6006	$179.60	$179.60	$179.60
Purchase #3	$160.40	6.531%	$170.8757	$170.88	$170.90	$170.90
Purchase #4	$248.36	10.815%	$275.2201	$275.22	$275.20	$275.20
Purchase #5	$86.89	5.558%	$91.7193	$91.72	$91.70	$91.70
Purchase #6	$16.65	4.222%	$17.353	$17.35	$17.35	$17.40
Purchase #7	$182.65	4.733%	$191.2948	$191.29	$191.30	$191.30
7 purchase totals =	$933.13		$1,003.8308	$1,003.83	$1,003.80	$1,003.90