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	$154.28	8.136%	$166.8322	$166.83	$166.85	$166.80
Purchase #2	$156.80	10.599%	$173.4192	$173.42	$173.40	$173.40
Purchase #3	$179.71	10.668%	$198.8815	$198.88	$198.90	$198.90
Purchase #4	$35.90	5.596%	$37.909	$37.91	$37.90	$37.90
Purchase #5	$90.81	5.766%	$96.0461	$96.05	$96.05	$96.00
Purchase #6	$179.53	4.210%	$187.0882	$187.09	$187.10	$187.10
Purchase #7	$34.62	12.139%	$38.8225	$38.82	$38.80	$38.80
7 purchase totals =	$831.65		$898.9987	$899.00	$899.00	$898.90