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	$90.28	6.851%	$96.4651	$96.47	$96.45	$96.50
Purchase #2	$207.98	10.531%	$229.8824	$229.88	$229.90	$229.90
Purchase #3	$172.29	6.830%	$184.0574	$184.06	$184.05	$184.10
Purchase #4	$153.79	7.847%	$165.8579	$165.86	$165.85	$165.90
Purchase #5	$225.32	7.679%	$242.6223	$242.62	$242.60	$242.60
Purchase #6	$131.47	10.185%	$144.8602	$144.86	$144.85	$144.90
Purchase #7	$139.37	10.592%	$154.1321	$154.13	$154.15	$154.10
7 purchase totals =	$1,120.50		$1,217.8774	$1,217.88	$1,217.85	$1,218.00