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	$46.97	6.182%	$49.8737	$49.87	$49.85	$49.90
Purchase #2	$79.48	9.807%	$87.2746	$87.27	$87.25	$87.30
Purchase #3	$248.59	12.394%	$279.4002	$279.40	$279.40	$279.40
Purchase #4	$48.54	12.367%	$54.5429	$54.54	$54.55	$54.50
Purchase #5	$10.76	7.577%	$11.5753	$11.58	$11.60	$11.60
Purchase #6	$200.89	5.308%	$211.5532	$211.55	$211.55	$211.60
Purchase #7	$136.41	4.471%	$142.5089	$142.51	$142.50	$142.50
7 purchase totals =	$771.64		$836.7288	$836.72	$836.70	$836.80