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	$127.55	3.720%	$132.2949	$132.29	$132.30	$132.30
Purchase #2	$47.73	13.507%	$54.1769	$54.18	$54.20	$54.20
Purchase #3	$73.51	10.845%	$81.4822	$81.48	$81.50	$81.50
Purchase #4	$246.79	7.712%	$265.8224	$265.82	$265.80	$265.80
Purchase #5	$54.28	9.331%	$59.3449	$59.34	$59.35	$59.30
Purchase #6	$101.66	5.522%	$107.2737	$107.27	$107.25	$107.30
Purchase #7	$173.57	10.388%	$191.6005	$191.60	$191.60	$191.60
7 purchase totals =	$825.09		$891.9955	$891.98	$892.00	$892.00