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	$123.94	6.161%	$131.5759	$131.58	$131.60	$131.60
Purchase #2	$158.37	6.587%	$168.8018	$168.80	$168.80	$168.80
Purchase #3	$204.60	5.597%	$216.0515	$216.05	$216.05	$216.10
Purchase #4	$193.93	10.510%	$214.312	$214.31	$214.30	$214.30
Purchase #5	$90.34	5.639%	$95.4343	$95.43	$95.45	$95.40
Purchase #6	$197.96	12.342%	$222.3922	$222.39	$222.40	$222.40
Purchase #7	$240.47	3.404%	$248.6556	$248.66	$248.65	$248.70
7 purchase totals =	$1,209.61		$1,297.2233	$1,297.22	$1,297.25	$1,297.30