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	$147.57	12.822%	$166.4914	$166.49	$166.50	$166.50
Purchase #2	$141.70	10.102%	$156.0145	$156.01	$156.00	$156.00
Purchase #3	$146.97	10.625%	$162.5856	$162.59	$162.60	$162.60
Purchase #4	$63.87	3.368%	$66.0211	$66.02	$66.00	$66.00
Purchase #5	$234.91	7.118%	$251.6309	$251.63	$251.65	$251.60
Purchase #6	$234.59	8.767%	$255.1565	$255.16	$255.15	$255.20
Purchase #7	$248.82	6.259%	$264.3936	$264.39	$264.40	$264.40
7 purchase totals =	$1,218.43		$1,322.2936	$1,322.29	$1,322.30	$1,322.30