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	$91.59	4.170%	$95.4093	$95.41	$95.40	$95.40
Purchase #2	$109.29	3.509%	$113.125	$113.13	$113.15	$113.10
Purchase #3	$72.55	10.281%	$80.0089	$80.01	$80.00	$80.00
Purchase #4	$80.98	10.732%	$89.6708	$89.67	$89.65	$89.70
Purchase #5	$58.69	13.621%	$66.6842	$66.68	$66.70	$66.70
Purchase #6	$127.92	11.179%	$142.2202	$142.22	$142.20	$142.20
Purchase #7	$18.41	5.235%	$19.3738	$19.37	$19.35	$19.40
7 purchase totals =	$559.43		$606.4922	$606.49	$606.45	$606.50