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	$154.54	8.859%	$168.2307	$168.23	$168.25	$168.20
Purchase #2	$153.79	9.383%	$168.2201	$168.22	$168.20	$168.20
Purchase #3	$207.85	6.644%	$221.6596	$221.66	$221.65	$221.70
Purchase #4	$139.88	4.770%	$146.5523	$146.55	$146.55	$146.60
Purchase #5	$133.39	3.116%	$137.5464	$137.55	$137.55	$137.50
Purchase #6	$7.86	4.499%	$8.2136	$8.21	$8.20	$8.20
Purchase #7	$38.83	4.510%	$40.5812	$40.58	$40.60	$40.60
7 purchase totals =	$836.14		$891.0039	$891.00	$891.00	$891.00