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	$145.40	8.557%	$157.8419	$157.84	$157.85	$157.80
Purchase #2	$164.31	5.591%	$173.4966	$173.50	$173.50	$173.50
Purchase #3	$228.89	4.677%	$239.5952	$239.60	$239.60	$239.60
Purchase #4	$47.31	12.848%	$53.3884	$53.39	$53.40	$53.40
Purchase #5	$183.30	3.542%	$189.7925	$189.79	$189.80	$189.80
Purchase #6	$118.88	10.848%	$131.7761	$131.78	$131.80	$131.80
Purchase #7	$51.34	12.776%	$57.8992	$57.90	$57.90	$57.90
7 purchase totals =	$939.43		$1,003.7899	$1,003.80	$1,003.85	$1,003.80