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	$151.47	12.403%	$170.2568	$170.26	$170.25	$170.30
Purchase #2	$42.58	6.194%	$45.2174	$45.22	$45.20	$45.20
Purchase #3	$173.51	6.766%	$185.2497	$185.25	$185.25	$185.20
Purchase #4	$129.51	10.681%	$143.343	$143.34	$143.35	$143.30
Purchase #5	$51.92	6.491%	$55.2901	$55.29	$55.30	$55.30
Purchase #6	$186.89	11.818%	$208.9767	$208.98	$209.00	$209.00
Purchase #7	$107.90	3.375%	$111.5416	$111.54	$111.55	$111.50
7 purchase totals =	$843.78		$919.8753	$919.88	$919.90	$919.80