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	$201.42	12.285%	$226.1644	$226.16	$226.15	$226.20
Purchase #2	$230.99	3.826%	$239.8277	$239.83	$239.85	$239.80
Purchase #3	$169.92	9.403%	$185.8976	$185.90	$185.90	$185.90
Purchase #4	$129.88	8.764%	$141.2627	$141.26	$141.25	$141.30
Purchase #5	$229.62	11.104%	$255.117	$255.12	$255.10	$255.10
Purchase #6	$89.25	12.379%	$100.2983	$100.30	$100.30	$100.30
Purchase #7	$129.46	7.823%	$139.5877	$139.59	$139.60	$139.60
7 purchase totals =	$1,180.54		$1,288.1554	$1,288.16	$1,288.15	$1,288.20