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	$115.69	7.711%	$124.6109	$124.61	$124.60	$124.60
Purchase #2	$153.65	3.391%	$158.8603	$158.86	$158.85	$158.90
Purchase #3	$246.56	5.766%	$260.7766	$260.78	$260.80	$260.80
Purchase #4	$244.76	13.791%	$278.5149	$278.51	$278.50	$278.50
Purchase #5	$178.30	7.768%	$192.1503	$192.15	$192.15	$192.20
Purchase #6	$210.40	3.812%	$218.4204	$218.42	$218.40	$218.40
Purchase #7	$41.35	13.258%	$46.8322	$46.83	$46.85	$46.80
7 purchase totals =	$1,190.71		$1,280.1656	$1,280.16	$1,280.15	$1,280.20