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	$23.89	10.158%	$26.3167	$26.32	$26.30	$26.30
Purchase #2	$104.91	6.299%	$111.5183	$111.52	$111.50	$111.50
Purchase #3	$32.40	5.805%	$34.2808	$34.28	$34.30	$34.30
Purchase #4	$101.68	6.219%	$108.0035	$108.00	$108.00	$108.00
Purchase #5	$174.57	7.847%	$188.2685	$188.27	$188.25	$188.30
Purchase #6	$81.61	13.460%	$92.5947	$92.59	$92.60	$92.60
Purchase #7	$60.44	10.345%	$66.6925	$66.69	$66.70	$66.70
7 purchase totals =	$579.50		$627.6750	$627.67	$627.65	$627.70