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	$111.60	11.456%	$124.3849	$124.38	$124.40	$124.40
Purchase #2	$76.75	7.555%	$82.5485	$82.55	$82.55	$82.50
Purchase #3	$201.26	3.602%	$208.5094	$208.51	$208.50	$208.50
Purchase #4	$34.95	7.271%	$37.4912	$37.49	$37.50	$37.50
Purchase #5	$185.34	3.130%	$191.1411	$191.14	$191.15	$191.10
Purchase #6	$177.77	5.517%	$187.5776	$187.58	$187.60	$187.60
Purchase #7	$55.53	4.230%	$57.8789	$57.88	$57.90	$57.90
7 purchase totals =	$843.20		$889.5316	$889.53	$889.60	$889.50