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	$146.50	6.700%	$156.3155	$156.32	$156.30	$156.30
Purchase #2	$229.57	11.187%	$255.252	$255.25	$255.25	$255.30
Purchase #3	$220.89	4.333%	$230.4612	$230.46	$230.45	$230.50
Purchase #4	$211.29	6.806%	$225.6704	$225.67	$225.65	$225.70
Purchase #5	$66.98	8.127%	$72.4235	$72.42	$72.40	$72.40
Purchase #6	$131.60	9.664%	$144.3178	$144.32	$144.30	$144.30
Purchase #7	$64.72	11.634%	$72.2495	$72.25	$72.25	$72.20
7 purchase totals =	$1,071.55		$1,156.6899	$1,156.69	$1,156.60	$1,156.70