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	$127.93	11.386%	$142.4961	$142.50	$142.50	$142.50
Purchase #2	$83.61	8.335%	$90.5789	$90.58	$90.60	$90.60
Purchase #3	$101.93	7.777%	$109.8571	$109.86	$109.85	$109.90
Purchase #4	$246.32	4.801%	$258.1458	$258.15	$258.15	$258.10
Purchase #5	$148.71	5.631%	$157.0839	$157.08	$157.10	$157.10
Purchase #6	$155.35	6.624%	$165.6404	$165.64	$165.65	$165.60
Purchase #7	$25.49	7.233%	$27.3337	$27.33	$27.35	$27.30
7 purchase totals =	$889.34		$951.1359	$951.14	$951.20	$951.10