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	$10.73	11.867%	$12.0033	$12.00	$12.00	$12.00
Purchase #2	$100.28	10.717%	$111.027	$111.03	$111.05	$111.00
Purchase #3	$235.74	6.655%	$251.4285	$251.43	$251.45	$251.40
Purchase #4	$130.33	3.493%	$134.8824	$134.88	$134.90	$134.90
Purchase #5	$87.31	4.196%	$90.9735	$90.97	$90.95	$91.00
Purchase #6	$214.67	13.172%	$242.9463	$242.95	$242.95	$242.90
Purchase #7	$44.40	3.461%	$45.9367	$45.94	$45.95	$45.90
7 purchase totals =	$823.46		$889.1977	$889.20	$889.25	$889.10