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	$55.95	5.861%	$59.2292	$59.23	$59.25	$59.20
Purchase #2	$133.43	13.818%	$151.8674	$151.87	$151.85	$151.90
Purchase #3	$19.36	7.464%	$20.805	$20.81	$20.80	$20.80
Purchase #4	$187.66	6.548%	$199.948	$199.95	$199.95	$199.90
Purchase #5	$167.94	11.821%	$187.7922	$187.79	$187.80	$187.80
Purchase #6	$29.95	7.652%	$32.2418	$32.24	$32.25	$32.20
Purchase #7	$38.80	12.394%	$43.6089	$43.61	$43.60	$43.60
7 purchase totals =	$633.09		$695.4925	$695.50	$695.50	$695.40