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	$241.89	12.615%	$272.4044	$272.40	$272.40	$272.40
Purchase #2	$40.68	5.863%	$43.0651	$43.07	$43.05	$43.10
Purchase #3	$176.67	6.604%	$188.3373	$188.34	$188.35	$188.30
Purchase #4	$9.60	12.642%	$10.8136	$10.81	$10.80	$10.80
Purchase #5	$151.32	12.361%	$170.0247	$170.02	$170.00	$170.00
Purchase #6	$153.71	8.172%	$166.2712	$166.27	$166.25	$166.30
Purchase #7	$85.40	5.820%	$90.3703	$90.37	$90.35	$90.40
7 purchase totals =	$859.27		$941.2866	$941.28	$941.20	$941.30