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	$72.61	9.194%	$79.2858	$79.29	$79.30	$79.30
Purchase #2	$146.97	10.449%	$162.3269	$162.33	$162.35	$162.30
Purchase #3	$150.39	5.414%	$158.5321	$158.53	$158.55	$158.50
Purchase #4	$55.79	9.598%	$61.1447	$61.14	$61.15	$61.10
Purchase #5	$48.56	3.423%	$50.2222	$50.22	$50.20	$50.20
Purchase #6	$124.42	11.388%	$138.5889	$138.59	$138.60	$138.60
Purchase #7	$73.25	12.797%	$82.6238	$82.62	$82.60	$82.60
7 purchase totals =	$671.99		$732.7244	$732.72	$732.75	$732.60