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	$68.89	13.249%	$78.0172	$78.02	$78.00	$78.00
Purchase #2	$209.87	4.256%	$218.8021	$218.80	$218.80	$218.80
Purchase #3	$49.52	6.862%	$52.9181	$52.92	$52.90	$52.90
Purchase #4	$16.54	10.506%	$18.2777	$18.28	$18.30	$18.30
Purchase #5	$185.69	13.548%	$210.8473	$210.85	$210.85	$210.80
Purchase #6	$241.48	11.178%	$268.4726	$268.47	$268.45	$268.50
Purchase #7	$22.85	13.314%	$25.8922	$25.89	$25.90	$25.90
7 purchase totals =	$794.84		$873.2272	$873.23	$873.20	$873.20