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	$8.70	13.443%	$9.8695	$9.87	$9.85	$9.90
Purchase #2	$213.61	9.462%	$233.8218	$233.82	$233.80	$233.80
Purchase #3	$187.88	13.200%	$212.6802	$212.68	$212.70	$212.70
Purchase #4	$72.40	13.481%	$82.1602	$82.16	$82.15	$82.20
Purchase #5	$40.96	13.711%	$46.576	$46.58	$46.60	$46.60
Purchase #6	$214.66	13.376%	$243.3729	$243.37	$243.35	$243.40
Purchase #7	$82.46	10.112%	$90.7984	$90.80	$90.80	$90.80
7 purchase totals =	$820.67		$919.2790	$919.28	$919.25	$919.40