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	$179.31	9.416%	$196.1938	$196.19	$196.20	$196.20
Purchase #2	$145.81	12.230%	$163.6426	$163.64	$163.65	$163.60
Purchase #3	$50.78	10.807%	$56.2678	$56.27	$56.25	$56.30
Purchase #4	$6.72	13.296%	$7.6135	$7.61	$7.60	$7.60
Purchase #5	$137.66	4.574%	$143.9566	$143.96	$143.95	$144.00
Purchase #6	$162.43	6.526%	$173.0302	$173.03	$173.05	$173.00
Purchase #7	$84.34	7.656%	$90.7971	$90.80	$90.80	$90.80
7 purchase totals =	$767.05		$831.5016	$831.50	$831.50	$831.50