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	$16.65	11.632%	$18.5867	$18.59	$18.60	$18.60
Purchase #2	$111.27	7.713%	$119.8523	$119.85	$119.85	$119.90
Purchase #3	$96.39	12.196%	$108.1457	$108.15	$108.15	$108.10
Purchase #4	$158.75	10.340%	$175.1648	$175.16	$175.15	$175.20
Purchase #5	$166.41	13.495%	$188.867	$188.87	$188.85	$188.90
Purchase #6	$226.32	5.354%	$238.4372	$238.44	$238.45	$238.40
Purchase #7	$147.71	6.443%	$157.227	$157.23	$157.25	$157.20
7 purchase totals =	$923.50		$1,006.2807	$1,006.29	$1,006.30	$1,006.30