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	$139.29	4.649%	$145.7656	$145.77	$145.75	$145.80
Purchase #2	$161.39	9.166%	$176.183	$176.18	$176.20	$176.20
Purchase #3	$101.69	9.604%	$111.4563	$111.46	$111.45	$111.50
Purchase #4	$164.43	9.304%	$179.7286	$179.73	$179.75	$179.70
Purchase #5	$155.98	5.604%	$164.7211	$164.72	$164.70	$164.70
Purchase #6	$229.32	13.732%	$260.8102	$260.81	$260.80	$260.80
Purchase #7	$99.74	12.570%	$112.2773	$112.28	$112.30	$112.30
7 purchase totals =	$1,051.84		$1,150.9421	$1,150.95	$1,150.95	$1,151.00