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	$228.44	13.680%	$259.6906	$259.69	$259.70	$259.70
Purchase #2	$150.68	11.591%	$168.1453	$168.15	$168.15	$168.10
Purchase #3	$139.36	4.131%	$145.117	$145.12	$145.10	$145.10
Purchase #4	$167.66	10.467%	$185.209	$185.21	$185.20	$185.20
Purchase #5	$247.67	7.440%	$266.0966	$266.10	$266.10	$266.10
Purchase #6	$132.29	11.791%	$147.8883	$147.89	$147.90	$147.90
Purchase #7	$128.94	11.263%	$143.4625	$143.46	$143.45	$143.50
7 purchase totals =	$1,195.04		$1,315.6093	$1,315.62	$1,315.60	$1,315.60