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	$99.71	8.806%	$108.4905	$108.49	$108.50	$108.50
Purchase #2	$218.74	4.654%	$228.9202	$228.92	$228.90	$228.90
Purchase #3	$173.38	3.770%	$179.9164	$179.92	$179.90	$179.90
Purchase #4	$83.77	7.508%	$90.0595	$90.06	$90.05	$90.10
Purchase #5	$186.43	13.153%	$210.9511	$210.95	$210.95	$211.00
Purchase #6	$239.57	3.831%	$248.7479	$248.75	$248.75	$248.70
Purchase #7	$18.25	7.353%	$19.5919	$19.59	$19.60	$19.60
7 purchase totals =	$1,019.85		$1,086.6775	$1,086.68	$1,086.65	$1,086.70