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	$105.78	3.241%	$109.2083	$109.21	$109.20	$109.20
Purchase #2	$64.62	12.371%	$72.6141	$72.61	$72.60	$72.60
Purchase #3	$105.77	12.824%	$119.3339	$119.33	$119.35	$119.30
Purchase #4	$41.39	13.641%	$47.036	$47.04	$47.05	$47.00
Purchase #5	$33.54	3.320%	$34.6535	$34.65	$34.65	$34.70
Purchase #6	$150.36	5.577%	$158.7456	$158.75	$158.75	$158.70
Purchase #7	$17.44	3.602%	$18.0682	$18.07	$18.05	$18.10
7 purchase totals =	$518.90		$559.6596	$559.66	$559.65	$559.60