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	$222.31	3.240%	$229.5128	$229.51	$229.50	$229.50
Purchase #2	$210.99	4.549%	$220.5879	$220.59	$220.60	$220.60
Purchase #3	$241.41	12.426%	$271.4076	$271.41	$271.40	$271.40
Purchase #4	$155.92	4.240%	$162.531	$162.53	$162.55	$162.50
Purchase #5	$156.89	11.286%	$174.5966	$174.60	$174.60	$174.60
Purchase #6	$21.61	12.316%	$24.2715	$24.27	$24.25	$24.30
Purchase #7	$124.31	6.676%	$132.6089	$132.61	$132.60	$132.60
7 purchase totals =	$1,133.44		$1,215.5163	$1,215.52	$1,215.50	$1,215.50