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	$92.50	12.302%	$103.8794	$103.88	$103.90	$103.90
Purchase #2	$232.52	12.868%	$262.4407	$262.44	$262.45	$262.40
Purchase #3	$171.60	11.247%	$190.8999	$190.90	$190.90	$190.90
Purchase #4	$155.85	11.578%	$173.8943	$173.89	$173.90	$173.90
Purchase #5	$77.27	4.123%	$80.4558	$80.46	$80.45	$80.50
Purchase #6	$135.59	6.262%	$144.0806	$144.08	$144.10	$144.10
Purchase #7	$173.27	7.459%	$186.1942	$186.19	$186.20	$186.20
7 purchase totals =	$1,038.60		$1,141.8449	$1,141.84	$1,141.90	$1,141.90