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	$84.77	5.657%	$89.5654	$89.57	$89.55	$89.60
Purchase #2	$138.28	6.323%	$147.0234	$147.02	$147.00	$147.00
Purchase #3	$91.42	9.327%	$99.9467	$99.95	$99.95	$99.90
Purchase #4	$206.69	11.560%	$230.5834	$230.58	$230.60	$230.60
Purchase #5	$85.29	7.675%	$91.836	$91.84	$91.85	$91.80
Purchase #6	$168.73	13.553%	$191.598	$191.60	$191.60	$191.60
Purchase #7	$54.43	7.505%	$58.515	$58.52	$58.50	$58.50
7 purchase totals =	$829.61		$909.0679	$909.08	$909.05	$909.00