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	$107.52	12.670%	$121.1428	$121.14	$121.15	$121.10
Purchase #2	$82.62	11.239%	$91.9057	$91.91	$91.90	$91.90
Purchase #3	$132.78	3.132%	$136.9387	$136.94	$136.95	$136.90
Purchase #4	$95.85	7.824%	$103.3493	$103.35	$103.35	$103.30
Purchase #5	$249.51	10.418%	$275.504	$275.50	$275.50	$275.50
Purchase #6	$59.25	13.711%	$67.3738	$67.37	$67.35	$67.40
Purchase #7	$48.78	10.412%	$53.859	$53.86	$53.85	$53.90
7 purchase totals =	$776.31		$850.0733	$850.07	$850.05	$850.00