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	$162.98	3.190%	$168.1791	$168.18	$168.20	$168.20
Purchase #2	$19.90	3.665%	$20.6293	$20.63	$20.65	$20.60
Purchase #3	$166.31	5.456%	$175.3839	$175.38	$175.40	$175.40
Purchase #4	$64.69	5.320%	$68.1315	$68.13	$68.15	$68.10
Purchase #5	$168.92	4.860%	$177.1295	$177.13	$177.15	$177.10
Purchase #6	$134.30	7.657%	$144.5834	$144.58	$144.60	$144.60
Purchase #7	$28.95	13.508%	$32.8606	$32.86	$32.85	$32.90
7 purchase totals =	$746.05		$786.8973	$786.89	$787.00	$786.90