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	$87.86	13.416%	$99.6473	$99.65	$99.65	$99.60
Purchase #2	$17.67	3.127%	$18.2225	$18.22	$18.20	$18.20
Purchase #3	$241.64	4.726%	$253.0599	$253.06	$253.05	$253.10
Purchase #4	$151.41	10.397%	$167.1521	$167.15	$167.15	$167.20
Purchase #5	$227.73	13.495%	$258.4622	$258.46	$258.45	$258.50
Purchase #6	$17.34	4.208%	$18.0697	$18.07	$18.05	$18.10
Purchase #7	$85.86	10.152%	$94.5765	$94.58	$94.60	$94.60
7 purchase totals =	$829.51		$909.1902	$909.19	$909.15	$909.30