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	$126.37	8.555%	$137.181	$137.18	$137.20	$137.20
Purchase #2	$27.63	6.645%	$29.466	$29.47	$29.45	$29.50
Purchase #3	$86.40	5.485%	$91.139	$91.14	$91.15	$91.10
Purchase #4	$250.47	11.661%	$279.6773	$279.68	$279.70	$279.70
Purchase #5	$215.34	6.689%	$229.7441	$229.74	$229.75	$229.70
Purchase #6	$99.52	13.380%	$112.8358	$112.84	$112.85	$112.80
Purchase #7	$103.45	7.367%	$111.0712	$111.07	$111.05	$111.10
7 purchase totals =	$909.18		$991.1144	$991.12	$991.15	$991.10