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	$220.62	3.745%	$228.8822	$228.88	$228.90	$228.90
Purchase #2	$145.26	13.675%	$165.1243	$165.12	$165.10	$165.10
Purchase #3	$20.72	4.530%	$21.6586	$21.66	$21.65	$21.70
Purchase #4	$241.95	11.206%	$269.0629	$269.06	$269.05	$269.10
Purchase #5	$42.36	3.131%	$43.6863	$43.69	$43.70	$43.70
Purchase #6	$84.28	6.606%	$89.8475	$89.85	$89.85	$89.80
Purchase #7	$12.28	4.655%	$12.8516	$12.85	$12.85	$12.90
7 purchase totals =	$767.47		$831.1134	$831.11	$831.10	$831.20