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	$43.48	13.588%	$49.3881	$49.39	$49.40	$49.40
Purchase #2	$163.65	4.171%	$170.4758	$170.48	$170.50	$170.50
Purchase #3	$110.39	12.530%	$124.2219	$124.22	$124.20	$124.20
Purchase #4	$107.72	3.303%	$111.278	$111.28	$111.30	$111.30
Purchase #5	$173.42	5.585%	$183.1055	$183.11	$183.10	$183.10
Purchase #6	$167.98	13.115%	$190.0106	$190.01	$190.00	$190.00
Purchase #7	$94.52	11.592%	$105.4768	$105.48	$105.50	$105.50
7 purchase totals =	$861.16		$933.9567	$933.97	$934.00	$934.00