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	$138.92	11.700%	$155.1736	$155.17	$155.15	$155.20
Purchase #2	$172.96	4.717%	$181.1185	$181.12	$181.10	$181.10
Purchase #3	$145.30	7.695%	$156.4808	$156.48	$156.50	$156.50
Purchase #4	$143.27	13.175%	$162.1458	$162.15	$162.15	$162.10
Purchase #5	$215.49	12.242%	$241.8703	$241.87	$241.85	$241.90
Purchase #6	$163.46	8.810%	$177.8608	$177.86	$177.85	$177.90
Purchase #7	$166.40	8.534%	$180.6006	$180.60	$180.60	$180.60
7 purchase totals =	$1,145.80		$1,255.2504	$1,255.25	$1,255.20	$1,255.30