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	$241.67	12.576%	$272.0624	$272.06	$272.05	$272.10
Purchase #2	$221.40	3.212%	$228.5114	$228.51	$228.50	$228.50
Purchase #3	$108.32	10.748%	$119.9622	$119.96	$119.95	$120.00
Purchase #4	$115.90	12.401%	$130.2728	$130.27	$130.25	$130.30
Purchase #5	$122.29	4.227%	$127.4592	$127.46	$127.45	$127.50
Purchase #6	$119.47	11.354%	$133.0346	$133.03	$133.05	$133.00
Purchase #7	$156.67	8.254%	$169.6015	$169.60	$169.60	$169.60
7 purchase totals =	$1,085.72		$1,180.9041	$1,180.89	$1,180.85	$1,181.00