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	$152.85	3.848%	$158.7317	$158.73	$158.75	$158.70
Purchase #2	$137.50	9.559%	$150.6436	$150.64	$150.65	$150.60
Purchase #3	$45.83	6.452%	$48.787	$48.79	$48.80	$48.80
Purchase #4	$33.94	11.162%	$37.7284	$37.73	$37.75	$37.70
Purchase #5	$52.32	3.590%	$54.1983	$54.20	$54.20	$54.20
Purchase #6	$34.62	4.851%	$36.2994	$36.30	$36.30	$36.30
Purchase #7	$160.43	12.566%	$180.5896	$180.59	$180.60	$180.60
7 purchase totals =	$617.49		$666.9780	$666.98	$667.05	$666.90