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	$223.69	7.103%	$239.5787	$239.58	$239.60	$239.60
Purchase #2	$172.86	11.774%	$193.2125	$193.21	$193.20	$193.20
Purchase #3	$123.27	6.661%	$131.481	$131.48	$131.50	$131.50
Purchase #4	$38.95	6.278%	$41.3953	$41.40	$41.40	$41.40
Purchase #5	$173.32	13.359%	$196.4738	$196.47	$196.45	$196.50
Purchase #6	$196.85	3.501%	$203.7417	$203.74	$203.75	$203.70
Purchase #7	$156.49	13.783%	$178.059	$178.06	$178.05	$178.10
7 purchase totals =	$1,085.43		$1,183.9420	$1,183.94	$1,183.95	$1,184.00