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	$226.88	12.617%	$255.5054	$255.51	$255.50	$255.50
Purchase #2	$173.60	3.411%	$179.5215	$179.52	$179.50	$179.50
Purchase #3	$61.93	9.732%	$67.957	$67.96	$67.95	$68.00
Purchase #4	$71.88	3.768%	$74.5884	$74.59	$74.60	$74.60
Purchase #5	$59.85	9.425%	$65.4909	$65.49	$65.50	$65.50
Purchase #6	$193.98	6.172%	$205.9524	$205.95	$205.95	$206.00
Purchase #7	$9.53	13.545%	$10.8208	$10.82	$10.80	$10.80
7 purchase totals =	$797.65		$859.8364	$859.84	$859.80	$859.90