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	$213.87	11.433%	$238.3218	$238.32	$238.30	$238.30
Purchase #2	$229.74	10.102%	$252.9483	$252.95	$252.95	$252.90
Purchase #3	$155.75	5.598%	$164.4689	$164.47	$164.45	$164.50
Purchase #4	$148.44	13.530%	$168.5239	$168.52	$168.50	$168.50
Purchase #5	$111.33	13.641%	$126.5165	$126.52	$126.50	$126.50
Purchase #6	$249.61	7.826%	$269.1445	$269.14	$269.15	$269.10
Purchase #7	$147.78	6.112%	$156.8123	$156.81	$156.80	$156.80
7 purchase totals =	$1,256.52		$1,376.7362	$1,376.73	$1,376.65	$1,376.60