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	$122.68	3.617%	$127.1173	$127.12	$127.10	$127.10
Purchase #2	$43.79	6.786%	$46.7616	$46.76	$46.75	$46.80
Purchase #3	$129.88	12.310%	$145.8682	$145.87	$145.85	$145.90
Purchase #4	$84.39	8.543%	$91.5994	$91.60	$91.60	$91.60
Purchase #5	$70.52	11.639%	$78.7278	$78.73	$78.75	$78.70
Purchase #6	$125.58	4.340%	$131.0302	$131.03	$131.05	$131.00
Purchase #7	$169.31	5.771%	$179.0809	$179.08	$179.10	$179.10
7 purchase totals =	$746.15		$800.1854	$800.19	$800.20	$800.20