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	$16.44	10.138%	$18.1067	$18.11	$18.10	$18.10
Purchase #2	$58.71	4.531%	$61.3702	$61.37	$61.35	$61.40
Purchase #3	$9.28	9.245%	$10.1379	$10.14	$10.15	$10.10
Purchase #4	$214.89	13.309%	$243.4897	$243.49	$243.50	$243.50
Purchase #5	$81.58	9.274%	$89.1457	$89.15	$89.15	$89.10
Purchase #6	$38.34	8.463%	$41.5847	$41.58	$41.60	$41.60
Purchase #7	$155.57	7.599%	$167.3918	$167.39	$167.40	$167.40
7 purchase totals =	$574.81		$631.2267	$631.23	$631.25	$631.20