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	$51.52	7.667%	$55.47	$55.47	$55.45	$55.50
Purchase #2	$117.35	8.639%	$127.4879	$127.49	$127.50	$127.50
Purchase #3	$120.34	6.482%	$128.1404	$128.14	$128.15	$128.10
Purchase #4	$61.27	12.610%	$68.9961	$69.00	$69.00	$69.00
Purchase #5	$61.27	6.670%	$65.3567	$65.36	$65.35	$65.40
Purchase #6	$10.92	13.683%	$12.4142	$12.41	$12.40	$12.40
Purchase #7	$171.48	8.173%	$185.4951	$185.50	$185.50	$185.50
7 purchase totals =	$594.15		$643.3604	$643.37	$643.35	$643.40