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	$68.29	8.795%	$74.2961	$74.30	$74.30	$74.30
Purchase #2	$201.97	7.532%	$217.1824	$217.18	$217.20	$217.20
Purchase #3	$83.92	6.640%	$89.4923	$89.49	$89.50	$89.50
Purchase #4	$63.54	12.105%	$71.2315	$71.23	$71.25	$71.20
Purchase #5	$241.34	6.610%	$257.2926	$257.29	$257.30	$257.30
Purchase #6	$54.65	9.175%	$59.6641	$59.66	$59.65	$59.70
Purchase #7	$24.71	10.676%	$27.348	$27.35	$27.35	$27.30
7 purchase totals =	$738.42		$796.5070	$796.50	$796.55	$796.50