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	$11.27	7.259%	$12.0881	$12.09	$12.10	$12.10
Purchase #2	$96.76	8.299%	$104.7901	$104.79	$104.80	$104.80
Purchase #3	$129.62	12.507%	$145.8316	$145.83	$145.85	$145.80
Purchase #4	$101.88	9.300%	$111.3548	$111.35	$111.35	$111.40
Purchase #5	$134.31	6.498%	$143.0375	$143.04	$143.05	$143.00
Purchase #6	$124.89	4.657%	$130.7061	$130.71	$130.70	$130.70
Purchase #7	$208.39	4.327%	$217.407	$217.41	$217.40	$217.40
7 purchase totals =	$807.12		$865.2152	$865.22	$865.25	$865.20