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	$98.62	10.798%	$109.269	$109.27	$109.25	$109.30
Purchase #2	$189.43	9.188%	$206.8348	$206.83	$206.85	$206.80
Purchase #3	$190.26	5.614%	$200.9412	$200.94	$200.95	$200.90
Purchase #4	$26.68	4.435%	$27.8633	$27.86	$27.85	$27.90
Purchase #5	$132.54	7.143%	$142.0073	$142.01	$142.00	$142.00
Purchase #6	$60.96	8.748%	$66.2928	$66.29	$66.30	$66.30
Purchase #7	$155.55	7.414%	$167.0825	$167.08	$167.10	$167.10
7 purchase totals =	$854.04		$920.2909	$920.28	$920.30	$920.30