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	$51.58	3.698%	$53.4874	$53.49	$53.50	$53.50
Purchase #2	$87.93	13.435%	$99.7434	$99.74	$99.75	$99.70
Purchase #3	$66.32	12.320%	$74.4906	$74.49	$74.50	$74.50
Purchase #4	$90.69	4.172%	$94.4736	$94.47	$94.45	$94.50
Purchase #5	$23.92	5.438%	$25.2208	$25.22	$25.20	$25.20
Purchase #6	$75.29	9.531%	$82.4659	$82.47	$82.45	$82.50
Purchase #7	$77.77	6.722%	$82.9977	$83.00	$83.00	$83.00
7 purchase totals =	$473.50		$512.8794	$512.88	$512.85	$512.90