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	$234.66	8.579%	$254.7915	$254.79	$254.80	$254.80
Purchase #2	$57.59	3.865%	$59.8159	$59.82	$59.80	$59.80
Purchase #3	$82.58	9.672%	$90.5671	$90.57	$90.55	$90.60
Purchase #4	$236.96	7.548%	$254.8457	$254.85	$254.85	$254.80
Purchase #5	$12.63	4.120%	$13.1504	$13.15	$13.15	$13.20
Purchase #6	$187.63	11.278%	$208.7909	$208.79	$208.80	$208.80
Purchase #7	$16.83	4.422%	$17.5742	$17.57	$17.55	$17.60
7 purchase totals =	$828.88		$899.5357	$899.54	$899.50	$899.60