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	$10.85	6.719%	$11.579	$11.58	$11.60	$11.60
Purchase #2	$209.36	10.579%	$231.5082	$231.51	$231.50	$231.50
Purchase #3	$182.57	9.854%	$200.5604	$200.56	$200.55	$200.60
Purchase #4	$104.72	9.378%	$114.5406	$114.54	$114.55	$114.50
Purchase #5	$134.82	4.819%	$141.317	$141.32	$141.30	$141.30
Purchase #6	$93.67	8.513%	$101.6441	$101.64	$101.65	$101.60
Purchase #7	$27.72	5.469%	$29.236	$29.24	$29.25	$29.20
7 purchase totals =	$763.71		$830.3853	$830.39	$830.40	$830.30