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	$223.31	3.613%	$231.3782	$231.38	$231.40	$231.40
Purchase #2	$35.38	13.545%	$40.1722	$40.17	$40.15	$40.20
Purchase #3	$127.40	13.703%	$144.8576	$144.86	$144.85	$144.90
Purchase #4	$23.66	3.709%	$24.5375	$24.54	$24.55	$24.50
Purchase #5	$204.74	8.437%	$222.0139	$222.01	$222.00	$222.00
Purchase #6	$136.72	6.154%	$145.1337	$145.13	$145.15	$145.10
Purchase #7	$169.43	6.871%	$181.0715	$181.07	$181.05	$181.10
7 purchase totals =	$920.64		$989.1646	$989.16	$989.15	$989.20