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	$172.64	4.707%	$180.7662	$180.77	$180.75	$180.80
Purchase #2	$241.77	3.785%	$250.921	$250.92	$250.90	$250.90
Purchase #3	$79.98	7.204%	$85.7418	$85.74	$85.75	$85.70
Purchase #4	$50.52	3.264%	$52.169	$52.17	$52.15	$52.20
Purchase #5	$208.32	11.852%	$233.0101	$233.01	$233.00	$233.00
Purchase #6	$65.89	12.683%	$74.2468	$74.25	$74.25	$74.20
Purchase #7	$85.95	3.626%	$89.0665	$89.07	$89.05	$89.10
7 purchase totals =	$905.07		$965.9214	$965.93	$965.85	$965.90