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	$50.44	11.581%	$56.2815	$56.28	$56.30	$56.30
Purchase #2	$159.50	6.187%	$169.3683	$169.37	$169.35	$169.40
Purchase #3	$160.89	5.198%	$169.2531	$169.25	$169.25	$169.30
Purchase #4	$139.87	3.118%	$144.2311	$144.23	$144.25	$144.20
Purchase #5	$153.49	12.436%	$172.578	$172.58	$172.60	$172.60
Purchase #6	$33.87	7.378%	$36.3689	$36.37	$36.35	$36.40
Purchase #7	$210.42	5.269%	$221.507	$221.51	$221.50	$221.50
7 purchase totals =	$908.48		$969.5879	$969.59	$969.60	$969.70