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	$66.55	12.414%	$74.8115	$74.81	$74.80	$74.80
Purchase #2	$242.79	3.309%	$250.8239	$250.82	$250.80	$250.80
Purchase #3	$79.66	9.574%	$87.2866	$87.29	$87.30	$87.30
Purchase #4	$55.85	7.107%	$59.8193	$59.82	$59.80	$59.80
Purchase #5	$214.98	13.606%	$244.2302	$244.23	$244.25	$244.20
Purchase #6	$179.58	7.784%	$193.5585	$193.56	$193.55	$193.60
Purchase #7	$94.26	12.192%	$105.7522	$105.75	$105.75	$105.80
7 purchase totals =	$933.67		$1,016.2822	$1,016.28	$1,016.25	$1,016.30