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	$28.52	9.181%	$31.1384	$31.14	$31.15	$31.10
Purchase #2	$67.44	10.267%	$74.3641	$74.36	$74.35	$74.40
Purchase #3	$185.40	3.560%	$192.0002	$192.00	$192.00	$192.00
Purchase #4	$188.56	4.204%	$196.4871	$196.49	$196.50	$196.50
Purchase #5	$30.32	13.693%	$34.4717	$34.47	$34.45	$34.50
Purchase #6	$41.83	8.261%	$45.2856	$45.29	$45.30	$45.30
Purchase #7	$64.99	11.873%	$72.7063	$72.71	$72.70	$72.70
7 purchase totals =	$607.06		$646.4534	$646.46	$646.45	$646.50