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	$79.86	13.153%	$90.364	$90.36	$90.35	$90.40
Purchase #2	$66.60	13.241%	$75.4185	$75.42	$75.40	$75.40
Purchase #3	$165.59	4.236%	$172.6044	$172.60	$172.60	$172.60
Purchase #4	$167.30	3.246%	$172.7306	$172.73	$172.75	$172.70
Purchase #5	$227.59	12.740%	$256.585	$256.59	$256.60	$256.60
Purchase #6	$37.60	3.826%	$39.0386	$39.04	$39.05	$39.00
Purchase #7	$17.98	12.287%	$20.1892	$20.19	$20.20	$20.20
7 purchase totals =	$762.52		$826.9303	$826.93	$826.95	$826.90