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	$160.28	3.325%	$165.6093	$165.61	$165.60	$165.60
Purchase #2	$96.58	4.382%	$100.8121	$100.81	$100.80	$100.80
Purchase #3	$146.72	7.572%	$157.8296	$157.83	$157.85	$157.80
Purchase #4	$217.30	5.217%	$228.6365	$228.64	$228.65	$228.60
Purchase #5	$140.72	3.483%	$145.6213	$145.62	$145.60	$145.60
Purchase #6	$52.44	4.783%	$54.9482	$54.95	$54.95	$54.90
Purchase #7	$48.27	10.502%	$53.3393	$53.34	$53.35	$53.30
7 purchase totals =	$862.31		$906.7963	$906.80	$906.80	$906.60