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	$79.84	6.611%	$85.1182	$85.12	$85.10	$85.10
Purchase #2	$41.80	9.383%	$45.7221	$45.72	$45.70	$45.70
Purchase #3	$127.83	10.458%	$141.1985	$141.20	$141.20	$141.20
Purchase #4	$33.47	12.195%	$37.5517	$37.55	$37.55	$37.60
Purchase #5	$192.77	13.379%	$218.5607	$218.56	$218.55	$218.60
Purchase #6	$107.94	7.644%	$116.1909	$116.19	$116.20	$116.20
Purchase #7	$32.48	10.862%	$36.008	$36.01	$36.00	$36.00
7 purchase totals =	$616.13		$680.3501	$680.35	$680.30	$680.40