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	$72.76	11.553%	$81.166	$81.17	$81.15	$81.20
Purchase #2	$62.79	12.259%	$70.4874	$70.49	$70.50	$70.50
Purchase #3	$16.78	5.819%	$17.7564	$17.76	$17.75	$17.80
Purchase #4	$17.33	12.752%	$19.5399	$19.54	$19.55	$19.50
Purchase #5	$137.51	9.673%	$150.8113	$150.81	$150.80	$150.80
Purchase #6	$134.69	7.564%	$144.878	$144.88	$144.90	$144.90
Purchase #7	$41.61	4.784%	$43.6006	$43.60	$43.60	$43.60
7 purchase totals =	$483.47		$528.2396	$528.25	$528.25	$528.30