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	$234.56	4.189%	$244.3857	$244.39	$244.40	$244.40
Purchase #2	$14.34	11.142%	$15.9378	$15.94	$15.95	$15.90
Purchase #3	$110.99	11.829%	$124.119	$124.12	$124.10	$124.10
Purchase #4	$79.32	12.472%	$89.2128	$89.21	$89.20	$89.20
Purchase #5	$51.87	9.540%	$56.8184	$56.82	$56.80	$56.80
Purchase #6	$179.69	9.295%	$196.3922	$196.39	$196.40	$196.40
Purchase #7	$149.68	10.235%	$164.9997	$165.00	$165.00	$165.00
7 purchase totals =	$820.45		$891.8656	$891.87	$891.85	$891.80