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	$84.82	5.328%	$89.3392	$89.34	$89.35	$89.30
Purchase #2	$30.97	5.305%	$32.613	$32.61	$32.60	$32.60
Purchase #3	$214.26	4.240%	$223.3446	$223.34	$223.35	$223.30
Purchase #4	$40.42	4.209%	$42.1213	$42.12	$42.10	$42.10
Purchase #5	$54.92	5.408%	$57.8901	$57.89	$57.90	$57.90
Purchase #6	$40.74	12.255%	$45.7327	$45.73	$45.75	$45.70
Purchase #7	$16.43	9.152%	$17.9337	$17.93	$17.95	$17.90
7 purchase totals =	$482.56		$508.9746	$508.96	$509.00	$508.80