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	$138.95	3.849%	$144.2982	$144.30	$144.30	$144.30
Purchase #2	$106.30	11.114%	$118.1142	$118.11	$118.10	$118.10
Purchase #3	$220.89	9.726%	$242.3738	$242.37	$242.35	$242.40
Purchase #4	$96.84	8.536%	$105.1063	$105.11	$105.10	$105.10
Purchase #5	$120.63	9.337%	$131.8932	$131.89	$131.90	$131.90
Purchase #6	$120.64	3.173%	$124.4679	$124.47	$124.45	$124.50
Purchase #7	$231.46	10.200%	$255.0689	$255.07	$255.05	$255.10
7 purchase totals =	$1,035.71		$1,121.3225	$1,121.32	$1,121.25	$1,121.40