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	$166.52	13.874%	$189.623	$189.62	$189.60	$189.60
Purchase #2	$59.66	3.784%	$61.9175	$61.92	$61.90	$61.90
Purchase #3	$168.59	5.319%	$177.5573	$177.56	$177.55	$177.60
Purchase #4	$139.29	3.373%	$143.9883	$143.99	$144.00	$144.00
Purchase #5	$73.83	13.140%	$83.5313	$83.53	$83.55	$83.50
Purchase #6	$192.47	6.655%	$205.2789	$205.28	$205.30	$205.30
Purchase #7	$133.32	5.714%	$140.9379	$140.94	$140.95	$140.90
7 purchase totals =	$933.68		$1,002.8342	$1,002.84	$1,002.85	$1,002.80