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	$144.56	10.649%	$159.9542	$159.95	$159.95	$160.00
Purchase #2	$204.79	4.316%	$213.6287	$213.63	$213.65	$213.60
Purchase #3	$97.91	10.709%	$108.3952	$108.40	$108.40	$108.40
Purchase #4	$67.89	3.743%	$70.4311	$70.43	$70.45	$70.40
Purchase #5	$89.89	13.255%	$101.8049	$101.80	$101.80	$101.80
Purchase #6	$65.95	9.605%	$72.2845	$72.28	$72.30	$72.30
Purchase #7	$127.43	13.680%	$144.8624	$144.86	$144.85	$144.90
7 purchase totals =	$798.42		$871.3610	$871.35	$871.40	$871.40