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	$164.60	9.477%	$180.1991	$180.20	$180.20	$180.20
Purchase #2	$60.57	7.169%	$64.9123	$64.91	$64.90	$64.90
Purchase #3	$52.86	11.861%	$59.1297	$59.13	$59.15	$59.10
Purchase #4	$152.93	13.348%	$173.3431	$173.34	$173.35	$173.30
Purchase #5	$17.82	6.222%	$18.9288	$18.93	$18.95	$18.90
Purchase #6	$21.72	7.227%	$23.2897	$23.29	$23.30	$23.30
Purchase #7	$207.39	5.546%	$218.8918	$218.89	$218.90	$218.90
7 purchase totals =	$677.89		$738.6945	$738.69	$738.75	$738.60