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	$127.61	3.533%	$132.1185	$132.12	$132.10	$132.10
Purchase #2	$195.32	9.336%	$213.5551	$213.56	$213.55	$213.60
Purchase #3	$106.37	7.370%	$114.2095	$114.21	$114.20	$114.20
Purchase #4	$198.78	13.714%	$226.0407	$226.04	$226.05	$226.00
Purchase #5	$30.61	9.383%	$33.4821	$33.48	$33.50	$33.50
Purchase #6	$107.44	3.828%	$111.5528	$111.55	$111.55	$111.60
Purchase #7	$123.79	4.143%	$128.9186	$128.92	$128.90	$128.90
7 purchase totals =	$889.92		$959.8773	$959.88	$959.85	$959.90