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	$82.46	10.296%	$90.9501	$90.95	$90.95	$91.00
Purchase #2	$141.95	4.671%	$148.5805	$148.58	$148.60	$148.60
Purchase #3	$123.33	7.575%	$132.6722	$132.67	$132.65	$132.70
Purchase #4	$166.98	12.509%	$187.8675	$187.87	$187.85	$187.90
Purchase #5	$55.87	3.508%	$57.8299	$57.83	$57.85	$57.80
Purchase #6	$16.49	10.691%	$18.2529	$18.25	$18.25	$18.30
Purchase #7	$238.37	5.152%	$250.6508	$250.65	$250.65	$250.70
7 purchase totals =	$825.45		$886.8039	$886.80	$886.80	$887.00