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	$16.63	11.379%	$18.5223	$18.52	$18.50	$18.50
Purchase #2	$186.52	5.350%	$196.4988	$196.50	$196.50	$196.50
Purchase #3	$144.87	5.337%	$152.6017	$152.60	$152.60	$152.60
Purchase #4	$102.80	6.241%	$109.2157	$109.22	$109.20	$109.20
Purchase #5	$243.93	5.244%	$256.7217	$256.72	$256.70	$256.70
Purchase #6	$106.95	5.495%	$112.8269	$112.83	$112.85	$112.80
Purchase #7	$186.90	4.340%	$195.0115	$195.01	$195.00	$195.00
7 purchase totals =	$988.60		$1,041.3986	$1,041.40	$1,041.35	$1,041.30