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	$123.97	12.324%	$139.2481	$139.25	$139.25	$139.20
Purchase #2	$144.30	3.668%	$149.5929	$149.59	$149.60	$149.60
Purchase #3	$57.40	13.466%	$65.1295	$65.13	$65.15	$65.10
Purchase #4	$10.37	7.735%	$11.1721	$11.17	$11.15	$11.20
Purchase #5	$172.94	12.651%	$194.8186	$194.82	$194.80	$194.80
Purchase #6	$239.87	6.835%	$256.2651	$256.27	$256.25	$256.30
Purchase #7	$99.81	12.769%	$112.5547	$112.55	$112.55	$112.60
7 purchase totals =	$848.66		$928.7810	$928.78	$928.75	$928.80