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	$83.35	8.590%	$90.5098	$90.51	$90.50	$90.50
Purchase #2	$173.42	12.254%	$194.6709	$194.67	$194.65	$194.70
Purchase #3	$75.86	8.322%	$82.1731	$82.17	$82.15	$82.20
Purchase #4	$151.33	4.328%	$157.8796	$157.88	$157.90	$157.90
Purchase #5	$132.60	13.611%	$150.6482	$150.65	$150.65	$150.60
Purchase #6	$165.45	4.485%	$172.8704	$172.87	$172.85	$172.90
Purchase #7	$221.52	3.726%	$229.7738	$229.77	$229.75	$229.80
7 purchase totals =	$1,003.53		$1,078.5258	$1,078.52	$1,078.45	$1,078.60