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	$122.96	11.150%	$136.67	$136.67	$136.65	$136.70
Purchase #2	$231.93	10.200%	$255.5869	$255.59	$255.60	$255.60
Purchase #3	$217.80	3.682%	$225.8194	$225.82	$225.80	$225.80
Purchase #4	$158.93	10.828%	$176.1389	$176.14	$176.15	$176.10
Purchase #5	$45.29	9.391%	$49.5432	$49.54	$49.55	$49.50
Purchase #6	$125.52	8.549%	$136.2507	$136.25	$136.25	$136.30
Purchase #7	$162.75	3.123%	$167.8327	$167.83	$167.85	$167.80
7 purchase totals =	$1,065.18		$1,147.8418	$1,147.84	$1,147.85	$1,147.80