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	$47.85	9.456%	$52.3747	$52.37	$52.35	$52.40
Purchase #2	$213.90	11.652%	$238.8236	$238.82	$238.80	$238.80
Purchase #3	$111.56	13.405%	$126.5146	$126.51	$126.50	$126.50
Purchase #4	$128.27	9.105%	$139.949	$139.95	$139.95	$139.90
Purchase #5	$105.41	4.545%	$110.2009	$110.20	$110.20	$110.20
Purchase #6	$156.64	3.659%	$162.3715	$162.37	$162.35	$162.40
Purchase #7	$55.97	7.457%	$60.1437	$60.14	$60.15	$60.10
7 purchase totals =	$819.60		$890.3780	$890.36	$890.30	$890.30