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	$42.30	10.553%	$46.7639	$46.76	$46.75	$46.80
Purchase #2	$65.52	13.514%	$74.3744	$74.37	$74.35	$74.40
Purchase #3	$246.52	7.454%	$264.8956	$264.90	$264.90	$264.90
Purchase #4	$207.83	10.327%	$229.2926	$229.29	$229.30	$229.30
Purchase #5	$12.25	5.423%	$12.9143	$12.91	$12.90	$12.90
Purchase #6	$91.30	10.229%	$100.6391	$100.64	$100.65	$100.60
Purchase #7	$69.73	7.431%	$74.9116	$74.91	$74.90	$74.90
7 purchase totals =	$735.45		$803.7915	$803.78	$803.75	$803.80