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	$37.82	5.805%	$40.0155	$40.02	$40.00	$40.00
Purchase #2	$78.30	6.202%	$83.1562	$83.16	$83.15	$83.20
Purchase #3	$41.69	9.672%	$45.7223	$45.72	$45.70	$45.70
Purchase #4	$11.62	4.146%	$12.1018	$12.10	$12.10	$12.10
Purchase #5	$39.56	10.829%	$43.844	$43.84	$43.85	$43.80
Purchase #6	$37.46	6.683%	$39.9635	$39.96	$39.95	$40.00
Purchase #7	$66.31	13.720%	$75.4077	$75.41	$75.40	$75.40
7 purchase totals =	$312.76		$340.2110	$340.21	$340.15	$340.20