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	$46.92	6.771%	$50.097	$50.10	$50.10	$50.10
Purchase #2	$132.76	12.619%	$149.513	$149.51	$149.50	$149.50
Purchase #3	$179.38	6.210%	$190.5195	$190.52	$190.50	$190.50
Purchase #4	$145.77	9.861%	$160.1444	$160.14	$160.15	$160.10
Purchase #5	$109.75	12.743%	$123.7354	$123.74	$123.75	$123.70
Purchase #6	$123.61	13.640%	$140.4704	$140.47	$140.45	$140.50
Purchase #7	$83.64	10.681%	$92.5736	$92.57	$92.55	$92.60
7 purchase totals =	$821.83		$907.0533	$907.05	$907.00	$907.00