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	$67.54	12.757%	$76.1561	$76.16	$76.15	$76.20
Purchase #2	$136.52	5.612%	$144.1815	$144.18	$144.20	$144.20
Purchase #3	$139.42	8.665%	$151.5007	$151.50	$151.50	$151.50
Purchase #4	$15.80	13.440%	$17.9235	$17.92	$17.90	$17.90
Purchase #5	$67.74	5.785%	$71.6588	$71.66	$71.65	$71.70
Purchase #6	$32.49	4.195%	$33.853	$33.85	$33.85	$33.90
Purchase #7	$41.97	10.818%	$46.5103	$46.51	$46.50	$46.50
7 purchase totals =	$501.48		$541.7839	$541.78	$541.75	$541.90