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	$132.33	11.140%	$147.0716	$147.07	$147.05	$147.10
Purchase #2	$66.60	5.292%	$70.1245	$70.12	$70.10	$70.10
Purchase #3	$147.28	3.647%	$152.6513	$152.65	$152.65	$152.70
Purchase #4	$165.90	10.291%	$182.9728	$182.97	$182.95	$183.00
Purchase #5	$22.59	10.227%	$24.9003	$24.90	$24.90	$24.90
Purchase #6	$100.56	10.512%	$111.1309	$111.13	$111.15	$111.10
Purchase #7	$112.48	3.280%	$116.1693	$116.17	$116.15	$116.20
7 purchase totals =	$747.74		$805.0207	$805.01	$804.95	$805.10