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	$112.51	13.596%	$127.8069	$127.81	$127.80	$127.80
Purchase #2	$85.63	11.347%	$95.3464	$95.35	$95.35	$95.30
Purchase #3	$185.74	10.105%	$204.509	$204.51	$204.50	$204.50
Purchase #4	$168.58	6.269%	$179.1483	$179.15	$179.15	$179.10
Purchase #5	$107.57	13.506%	$122.0984	$122.10	$122.10	$122.10
Purchase #6	$217.92	9.455%	$238.5243	$238.52	$238.50	$238.50
Purchase #7	$8.96	13.244%	$10.1467	$10.15	$10.15	$10.10
7 purchase totals =	$886.91		$977.5800	$977.59	$977.55	$977.40