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	$150.28	12.117%	$168.4894	$168.49	$168.50	$168.50
Purchase #2	$168.38	7.654%	$181.2678	$181.27	$181.25	$181.30
Purchase #3	$196.85	12.140%	$220.7476	$220.75	$220.75	$220.70
Purchase #4	$204.75	11.654%	$228.6116	$228.61	$228.60	$228.60
Purchase #5	$46.66	13.433%	$52.9278	$52.93	$52.95	$52.90
Purchase #6	$229.96	9.510%	$251.8292	$251.83	$251.85	$251.80
Purchase #7	$180.94	4.849%	$189.7138	$189.71	$189.70	$189.70
7 purchase totals =	$1,177.82		$1,293.5872	$1,293.59	$1,293.60	$1,293.50