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	$28.51	10.531%	$31.5124	$31.51	$31.50	$31.50
Purchase #2	$227.26	5.642%	$240.082	$240.08	$240.10	$240.10
Purchase #3	$116.52	9.732%	$127.8597	$127.86	$127.85	$127.90
Purchase #4	$138.66	12.841%	$156.4653	$156.47	$156.45	$156.50
Purchase #5	$61.45	9.401%	$67.2269	$67.23	$67.25	$67.20
Purchase #6	$212.68	6.697%	$226.9232	$226.92	$226.90	$226.90
Purchase #7	$71.85	8.519%	$77.9709	$77.97	$77.95	$78.00
7 purchase totals =	$856.93		$928.0404	$928.04	$928.00	$928.10