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	$185.88	3.624%	$192.6163	$192.62	$192.60	$192.60
Purchase #2	$220.92	3.587%	$228.8444	$228.84	$228.85	$228.80
Purchase #3	$21.51	7.148%	$23.0475	$23.05	$23.05	$23.00
Purchase #4	$59.53	12.341%	$66.8766	$66.88	$66.90	$66.90
Purchase #5	$50.60	12.476%	$56.9129	$56.91	$56.90	$56.90
Purchase #6	$73.96	12.109%	$82.9158	$82.92	$82.90	$82.90
Purchase #7	$20.49	4.344%	$21.3801	$21.38	$21.40	$21.40
7 purchase totals =	$632.89		$672.5936	$672.60	$672.60	$672.50