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	$19.45	4.496%	$20.3245	$20.32	$20.30	$20.30
Purchase #2	$40.32	6.657%	$43.0041	$43.00	$43.00	$43.00
Purchase #3	$19.51	3.265%	$20.147	$20.15	$20.15	$20.10
Purchase #4	$214.56	12.141%	$240.6097	$240.61	$240.60	$240.60
Purchase #5	$24.84	6.255%	$26.3937	$26.39	$26.40	$26.40
Purchase #6	$58.82	11.492%	$65.5796	$65.58	$65.60	$65.60
Purchase #7	$71.66	7.642%	$77.1363	$77.14	$77.15	$77.10
7 purchase totals =	$449.16		$493.1949	$493.19	$493.20	$493.10