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	$129.60	4.180%	$135.0173	$135.02	$135.00	$135.00
Purchase #2	$64.36	12.538%	$72.4295	$72.43	$72.45	$72.40
Purchase #3	$145.86	4.720%	$152.7446	$152.74	$152.75	$152.70
Purchase #4	$148.61	5.707%	$157.0912	$157.09	$157.10	$157.10
Purchase #5	$37.33	5.836%	$39.5086	$39.51	$39.50	$39.50
Purchase #6	$246.45	9.247%	$269.2392	$269.24	$269.25	$269.20
Purchase #7	$20.72	4.131%	$21.5759	$21.58	$21.60	$21.60
7 purchase totals =	$792.93		$847.6063	$847.61	$847.65	$847.50