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	$58.59	13.533%	$66.519	$66.52	$66.50	$66.50
Purchase #2	$128.87	10.692%	$142.6488	$142.65	$142.65	$142.60
Purchase #3	$120.59	11.750%	$134.7593	$134.76	$134.75	$134.80
Purchase #4	$71.42	11.675%	$79.7583	$79.76	$79.75	$79.80
Purchase #5	$209.33	12.660%	$235.8312	$235.83	$235.85	$235.80
Purchase #6	$33.82	13.641%	$38.4334	$38.43	$38.45	$38.40
Purchase #7	$44.82	12.189%	$50.2831	$50.28	$50.30	$50.30
7 purchase totals =	$667.44		$748.2331	$748.23	$748.25	$748.20