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	$245.25	11.130%	$272.5463	$272.55	$272.55	$272.50
Purchase #2	$92.71	13.784%	$105.4891	$105.49	$105.50	$105.50
Purchase #3	$48.51	10.576%	$53.6404	$53.64	$53.65	$53.60
Purchase #4	$41.90	3.341%	$43.2999	$43.30	$43.30	$43.30
Purchase #5	$12.42	7.659%	$13.3712	$13.37	$13.35	$13.40
Purchase #6	$138.98	10.251%	$153.2268	$153.23	$153.25	$153.20
Purchase #7	$153.53	5.781%	$162.4056	$162.41	$162.40	$162.40
7 purchase totals =	$733.30		$803.9793	$803.99	$804.00	$803.90