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	$49.42	3.628%	$51.213	$51.21	$51.20	$51.20
Purchase #2	$98.71	10.697%	$109.269	$109.27	$109.25	$109.30
Purchase #3	$146.59	13.804%	$166.8253	$166.83	$166.85	$166.80
Purchase #4	$120.27	5.439%	$126.8115	$126.81	$126.80	$126.80
Purchase #5	$220.40	9.784%	$241.9639	$241.96	$241.95	$242.00
Purchase #6	$53.31	10.801%	$59.068	$59.07	$59.05	$59.10
Purchase #7	$23.27	4.833%	$24.3946	$24.39	$24.40	$24.40
7 purchase totals =	$711.97		$779.5453	$779.54	$779.50	$779.60