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	$62.50	6.565%	$66.6031	$66.60	$66.60	$66.60
Purchase #2	$59.92	6.511%	$63.8214	$63.82	$63.80	$63.80
Purchase #3	$109.64	6.105%	$116.3335	$116.33	$116.35	$116.30
Purchase #4	$184.56	10.308%	$203.5844	$203.58	$203.60	$203.60
Purchase #5	$111.39	10.506%	$123.0926	$123.09	$123.10	$123.10
Purchase #6	$98.59	7.837%	$106.3165	$106.32	$106.30	$106.30
Purchase #7	$93.68	11.728%	$104.6668	$104.67	$104.65	$104.70
7 purchase totals =	$720.28		$784.4183	$784.41	$784.40	$784.40