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	$204.57	10.104%	$225.2398	$225.24	$225.25	$225.20
Purchase #2	$165.32	8.518%	$179.402	$179.40	$179.40	$179.40
Purchase #3	$14.94	4.349%	$15.5897	$15.59	$15.60	$15.60
Purchase #4	$213.51	13.148%	$241.5823	$241.58	$241.60	$241.60
Purchase #5	$105.94	10.295%	$116.8465	$116.85	$116.85	$116.80
Purchase #6	$57.86	5.658%	$61.1337	$61.13	$61.15	$61.10
Purchase #7	$38.61	5.793%	$40.8467	$40.85	$40.85	$40.80
7 purchase totals =	$800.75		$880.6407	$880.64	$880.70	$880.50