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	$138.76	13.688%	$157.7535	$157.75	$157.75	$157.80
Purchase #2	$37.88	7.539%	$40.7358	$40.74	$40.75	$40.70
Purchase #3	$96.33	9.238%	$105.229	$105.23	$105.25	$105.20
Purchase #4	$152.31	12.819%	$171.8346	$171.83	$171.85	$171.80
Purchase #5	$32.62	6.866%	$34.8597	$34.86	$34.85	$34.90
Purchase #6	$90.84	6.835%	$97.0489	$97.05	$97.05	$97.00
Purchase #7	$10.32	5.733%	$10.9116	$10.91	$10.90	$10.90
7 purchase totals =	$559.06		$618.3731	$618.37	$618.40	$618.30