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	$142.57	8.777%	$155.0834	$155.08	$155.10	$155.10
Purchase #2	$49.37	12.565%	$55.5733	$55.57	$55.55	$55.60
Purchase #3	$31.52	10.456%	$34.8157	$34.82	$34.80	$34.80
Purchase #4	$216.57	7.521%	$232.8582	$232.86	$232.85	$232.90
Purchase #5	$87.25	5.280%	$91.8568	$91.86	$91.85	$91.90
Purchase #6	$100.97	13.388%	$114.4879	$114.49	$114.50	$114.50
Purchase #7	$49.61	9.391%	$54.2689	$54.27	$54.25	$54.30
7 purchase totals =	$677.86		$738.9442	$738.95	$738.90	$739.10