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	$225.39	5.419%	$237.6039	$237.60	$237.60	$237.60
Purchase #2	$84.47	3.747%	$87.6351	$87.64	$87.65	$87.60
Purchase #3	$231.30	5.375%	$243.7324	$243.73	$243.75	$243.70
Purchase #4	$58.58	5.135%	$61.5881	$61.59	$61.60	$61.60
Purchase #5	$13.65	13.706%	$15.5209	$15.52	$15.50	$15.50
Purchase #6	$173.90	13.190%	$196.8374	$196.84	$196.85	$196.80
Purchase #7	$122.94	6.748%	$131.236	$131.24	$131.25	$131.20
7 purchase totals =	$910.23		$974.1538	$974.16	$974.20	$974.00