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	$38.65	11.310%	$43.0213	$43.02	$43.00	$43.00
Purchase #2	$116.29	5.370%	$122.5348	$122.53	$122.55	$122.50
Purchase #3	$103.75	5.618%	$109.5787	$109.58	$109.60	$109.60
Purchase #4	$90.88	10.137%	$100.0925	$100.09	$100.10	$100.10
Purchase #5	$130.33	12.124%	$146.1312	$146.13	$146.15	$146.10
Purchase #6	$61.48	8.869%	$66.9327	$66.93	$66.95	$66.90
Purchase #7	$22.65	6.528%	$24.1286	$24.13	$24.15	$24.10
7 purchase totals =	$564.03		$612.4198	$612.41	$612.50	$612.30