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	$169.50	9.277%	$185.2245	$185.22	$185.20	$185.20
Purchase #2	$43.61	4.211%	$45.4464	$45.45	$45.45	$45.40
Purchase #3	$189.65	9.345%	$207.3728	$207.37	$207.35	$207.40
Purchase #4	$54.87	13.713%	$62.3943	$62.39	$62.40	$62.40
Purchase #5	$46.68	6.111%	$49.5326	$49.53	$49.55	$49.50
Purchase #6	$27.79	3.721%	$28.8241	$28.82	$28.80	$28.80
Purchase #7	$81.68	4.501%	$85.3564	$85.36	$85.35	$85.40
7 purchase totals =	$613.78		$664.1511	$664.14	$664.10	$664.10