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	$36.31	10.595%	$40.157	$40.16	$40.15	$40.20
Purchase #2	$130.60	9.490%	$142.9939	$142.99	$143.00	$143.00
Purchase #3	$132.57	5.414%	$139.7473	$139.75	$139.75	$139.70
Purchase #4	$151.45	11.797%	$169.3166	$169.32	$169.30	$169.30
Purchase #5	$152.35	13.773%	$173.3332	$173.33	$173.35	$173.30
Purchase #6	$168.49	10.230%	$185.7265	$185.73	$185.75	$185.70
Purchase #7	$37.25	12.466%	$41.8936	$41.89	$41.90	$41.90
7 purchase totals =	$809.02		$893.1681	$893.17	$893.20	$893.10