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	$247.70	4.393%	$258.5815	$258.58	$258.60	$258.60
Purchase #2	$50.84	4.606%	$53.1817	$53.18	$53.20	$53.20
Purchase #3	$25.37	13.282%	$28.7396	$28.74	$28.75	$28.70
Purchase #4	$48.96	11.323%	$54.5037	$54.50	$54.50	$54.50
Purchase #5	$230.33	4.255%	$240.1305	$240.13	$240.15	$240.10
Purchase #6	$74.89	11.846%	$83.7615	$83.76	$83.75	$83.80
Purchase #7	$91.69	8.362%	$99.3571	$99.36	$99.35	$99.40
7 purchase totals =	$769.78		$818.2556	$818.25	$818.30	$818.30