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	$12.35	4.338%	$12.8857	$12.89	$12.90	$12.90
Purchase #2	$60.90	9.795%	$66.8652	$66.87	$66.85	$66.90
Purchase #3	$217.30	6.423%	$231.2572	$231.26	$231.25	$231.30
Purchase #4	$128.41	12.660%	$144.6667	$144.67	$144.65	$144.70
Purchase #5	$89.99	7.166%	$96.4387	$96.44	$96.45	$96.40
Purchase #6	$99.99	11.557%	$111.5458	$111.55	$111.55	$111.50
Purchase #7	$76.58	7.402%	$82.2485	$82.25	$82.25	$82.20
7 purchase totals =	$685.52		$745.9078	$745.93	$745.90	$745.90