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	$37.98	4.241%	$39.5907	$39.59	$39.60	$39.60
Purchase #2	$170.28	4.704%	$178.29	$178.29	$178.30	$178.30
Purchase #3	$13.78	10.708%	$15.2556	$15.26	$15.25	$15.30
Purchase #4	$88.90	7.312%	$95.4004	$95.40	$95.40	$95.40
Purchase #5	$178.99	12.261%	$200.936	$200.94	$200.95	$200.90
Purchase #6	$159.31	3.669%	$165.1551	$165.16	$165.15	$165.20
Purchase #7	$137.34	10.505%	$151.7676	$151.77	$151.75	$151.80
7 purchase totals =	$786.58		$846.3954	$846.41	$846.40	$846.50