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	$184.82	4.475%	$193.0907	$193.09	$193.10	$193.10
Purchase #2	$56.47	8.583%	$61.3168	$61.32	$61.30	$61.30
Purchase #3	$228.95	9.429%	$250.5377	$250.54	$250.55	$250.50
Purchase #4	$153.31	5.567%	$161.8448	$161.84	$161.85	$161.80
Purchase #5	$35.93	4.418%	$37.5174	$37.52	$37.50	$37.50
Purchase #6	$31.63	3.854%	$32.849	$32.85	$32.85	$32.80
Purchase #7	$227.95	13.552%	$258.8418	$258.84	$258.85	$258.80
7 purchase totals =	$919.06		$995.9982	$996.00	$996.00	$995.80