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	$165.85	13.370%	$188.0241	$188.02	$188.00	$188.00
Purchase #2	$71.31	7.368%	$76.5641	$76.56	$76.55	$76.60
Purchase #3	$166.54	10.189%	$183.5088	$183.51	$183.50	$183.50
Purchase #4	$217.85	9.314%	$238.1405	$238.14	$238.15	$238.10
Purchase #5	$134.83	6.659%	$143.8083	$143.81	$143.80	$143.80
Purchase #6	$168.67	11.225%	$187.6032	$187.60	$187.60	$187.60
Purchase #7	$248.93	9.541%	$272.6804	$272.68	$272.70	$272.70
7 purchase totals =	$1,173.98		$1,290.3294	$1,290.32	$1,290.30	$1,290.30