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	$66.42	9.741%	$72.89	$72.89	$72.90	$72.90
Purchase #2	$166.63	11.321%	$185.4942	$185.49	$185.50	$185.50
Purchase #3	$229.77	6.253%	$244.1375	$244.14	$244.15	$244.10
Purchase #4	$44.86	7.113%	$48.0509	$48.05	$48.05	$48.10
Purchase #5	$194.40	11.551%	$216.8551	$216.86	$216.85	$216.90
Purchase #6	$36.72	7.721%	$39.5552	$39.56	$39.55	$39.60
Purchase #7	$61.40	8.539%	$66.6429	$66.64	$66.65	$66.60
7 purchase totals =	$800.20		$873.6258	$873.63	$873.65	$873.70