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	$83.64	6.660%	$89.2104	$89.21	$89.20	$89.20
Purchase #2	$124.68	3.296%	$128.7895	$128.79	$128.80	$128.80
Purchase #3	$90.45	10.140%	$99.6216	$99.62	$99.60	$99.60
Purchase #4	$109.78	6.381%	$116.7851	$116.79	$116.80	$116.80
Purchase #5	$148.38	13.212%	$167.984	$167.98	$168.00	$168.00
Purchase #6	$143.74	5.464%	$151.594	$151.59	$151.60	$151.60
Purchase #7	$132.51	5.225%	$139.4336	$139.43	$139.45	$139.40
7 purchase totals =	$833.18		$893.4182	$893.41	$893.45	$893.40