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	$66.77	6.515%	$71.1201	$71.12	$71.10	$71.10
Purchase #2	$116.57	13.492%	$132.2976	$132.30	$132.30	$132.30
Purchase #3	$65.34	10.366%	$72.1131	$72.11	$72.10	$72.10
Purchase #4	$211.28	4.688%	$221.1848	$221.18	$221.20	$221.20
Purchase #5	$241.39	5.824%	$255.4486	$255.45	$255.45	$255.40
Purchase #6	$166.41	8.106%	$179.8992	$179.90	$179.90	$179.90
Purchase #7	$20.75	11.237%	$23.0817	$23.08	$23.10	$23.10
7 purchase totals =	$888.51		$955.1451	$955.14	$955.15	$955.10