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	$132.38	10.658%	$146.4891	$146.49	$146.50	$146.50
Purchase #2	$131.83	8.385%	$142.8839	$142.88	$142.90	$142.90
Purchase #3	$25.99	8.146%	$28.1071	$28.11	$28.10	$28.10
Purchase #4	$33.97	12.268%	$38.1374	$38.14	$38.15	$38.10
Purchase #5	$135.59	4.139%	$141.2021	$141.20	$141.20	$141.20
Purchase #6	$9.27	13.188%	$10.4925	$10.49	$10.50	$10.50
Purchase #7	$130.52	6.497%	$138.9999	$139.00	$139.00	$139.00
7 purchase totals =	$599.55		$646.3120	$646.31	$646.35	$646.30