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	$81.44	11.286%	$90.6313	$90.63	$90.65	$90.60
Purchase #2	$17.45	5.826%	$18.4666	$18.47	$18.45	$18.50
Purchase #3	$68.79	13.520%	$78.0904	$78.09	$78.10	$78.10
Purchase #4	$14.54	7.399%	$15.6158	$15.62	$15.60	$15.60
Purchase #5	$75.62	11.324%	$84.1832	$84.18	$84.20	$84.20
Purchase #6	$118.68	10.690%	$131.3669	$131.37	$131.35	$131.40
Purchase #7	$235.81	8.341%	$255.4789	$255.48	$255.50	$255.50
7 purchase totals =	$612.33		$673.8331	$673.84	$673.85	$673.90