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	$231.61	9.200%	$252.9181	$252.92	$252.90	$252.90
Purchase #2	$111.81	13.255%	$126.6304	$126.63	$126.65	$126.60
Purchase #3	$179.29	5.563%	$189.2639	$189.26	$189.25	$189.30
Purchase #4	$226.47	13.391%	$256.7966	$256.80	$256.80	$256.80
Purchase #5	$128.38	3.483%	$132.8515	$132.85	$132.85	$132.90
Purchase #6	$213.32	4.485%	$222.8874	$222.89	$222.90	$222.90
Purchase #7	$95.53	3.549%	$98.9204	$98.92	$98.90	$98.90
7 purchase totals =	$1,186.41		$1,280.2683	$1,280.27	$1,280.25	$1,280.30