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	$15.67	11.775%	$17.5151	$17.52	$17.50	$17.50
Purchase #2	$131.72	3.483%	$136.3078	$136.31	$136.30	$136.30
Purchase #3	$15.58	11.121%	$17.3127	$17.31	$17.30	$17.30
Purchase #4	$133.88	13.421%	$151.848	$151.85	$151.85	$151.80
Purchase #5	$101.73	9.460%	$111.3537	$111.35	$111.35	$111.40
Purchase #6	$146.97	5.109%	$154.4787	$154.48	$154.50	$154.50
Purchase #7	$221.45	5.576%	$233.7981	$233.80	$233.80	$233.80
7 purchase totals =	$767.00		$822.6141	$822.62	$822.60	$822.60