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	$89.41	11.388%	$99.592	$99.59	$99.60	$99.60
Purchase #2	$41.82	6.283%	$44.4476	$44.45	$44.45	$44.40
Purchase #3	$240.39	13.139%	$271.9748	$271.97	$271.95	$272.00
Purchase #4	$99.83	11.730%	$111.5401	$111.54	$111.55	$111.50
Purchase #5	$60.27	10.112%	$66.3645	$66.36	$66.35	$66.40
Purchase #6	$25.82	13.369%	$29.2719	$29.27	$29.25	$29.30
Purchase #7	$99.80	12.621%	$112.3958	$112.40	$112.40	$112.40
7 purchase totals =	$657.34		$735.5867	$735.58	$735.55	$735.60