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	$228.31	9.709%	$250.4766	$250.48	$250.50	$250.50
Purchase #2	$54.28	4.105%	$56.5082	$56.51	$56.50	$56.50
Purchase #3	$125.68	12.607%	$141.5245	$141.52	$141.50	$141.50
Purchase #4	$112.27	10.872%	$124.476	$124.48	$124.50	$124.50
Purchase #5	$136.43	9.332%	$149.1616	$149.16	$149.15	$149.20
Purchase #6	$59.47	6.718%	$63.4652	$63.47	$63.45	$63.50
Purchase #7	$223.59	3.257%	$230.8723	$230.87	$230.85	$230.90
7 purchase totals =	$940.03		$1,016.4844	$1,016.49	$1,016.45	$1,016.60