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	$239.59	3.551%	$248.0978	$248.10	$248.10	$248.10
Purchase #2	$15.69	10.740%	$17.3751	$17.38	$17.40	$17.40
Purchase #3	$181.98	5.824%	$192.5785	$192.58	$192.60	$192.60
Purchase #4	$86.78	4.523%	$90.7051	$90.71	$90.70	$90.70
Purchase #5	$53.38	6.530%	$56.8657	$56.87	$56.85	$56.90
Purchase #6	$65.52	7.517%	$70.4451	$70.45	$70.45	$70.40
Purchase #7	$90.93	4.630%	$95.1401	$95.14	$95.15	$95.10
7 purchase totals =	$733.87		$771.2074	$771.23	$771.25	$771.20