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	$24.45	9.581%	$26.7926	$26.79	$26.80	$26.80
Purchase #2	$52.44	13.354%	$59.4428	$59.44	$59.45	$59.40
Purchase #3	$125.72	9.617%	$137.8105	$137.81	$137.80	$137.80
Purchase #4	$159.28	8.476%	$172.7806	$172.78	$172.80	$172.80
Purchase #5	$164.58	13.224%	$186.3441	$186.34	$186.35	$186.30
Purchase #6	$92.60	11.700%	$103.4342	$103.43	$103.45	$103.40
Purchase #7	$180.31	10.522%	$199.2822	$199.28	$199.30	$199.30
7 purchase totals =	$799.38		$885.8870	$885.87	$885.95	$885.80