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	$90.71	8.692%	$98.5945	$98.59	$98.60	$98.60
Purchase #2	$164.49	9.468%	$180.0639	$180.06	$180.05	$180.10
Purchase #3	$169.67	10.257%	$187.0731	$187.07	$187.05	$187.10
Purchase #4	$113.81	11.125%	$126.4714	$126.47	$126.45	$126.50
Purchase #5	$90.71	13.847%	$103.2706	$103.27	$103.25	$103.30
Purchase #6	$166.75	8.277%	$180.5519	$180.55	$180.55	$180.60
Purchase #7	$92.71	13.139%	$104.8912	$104.89	$104.90	$104.90
7 purchase totals =	$888.85		$980.9166	$980.90	$980.85	$981.10