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	$72.67	13.569%	$82.5306	$82.53	$82.55	$82.50
Purchase #2	$199.27	4.514%	$208.265	$208.27	$208.25	$208.30
Purchase #3	$121.37	10.262%	$133.825	$133.83	$133.85	$133.80
Purchase #4	$34.46	4.190%	$35.9039	$35.90	$35.90	$35.90
Purchase #5	$199.68	11.871%	$223.384	$223.38	$223.40	$223.40
Purchase #6	$152.58	12.831%	$172.1575	$172.16	$172.15	$172.20
Purchase #7	$49.67	9.689%	$54.4825	$54.48	$54.50	$54.50
7 purchase totals =	$829.70		$910.5485	$910.55	$910.60	$910.60