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	$73.92	12.853%	$83.4209	$83.42	$83.40	$83.40
Purchase #2	$111.87	11.513%	$124.7496	$124.75	$124.75	$124.70
Purchase #3	$127.65	3.778%	$132.4726	$132.47	$132.45	$132.50
Purchase #4	$103.30	3.224%	$106.6304	$106.63	$106.65	$106.60
Purchase #5	$194.58	13.796%	$221.4243	$221.42	$221.40	$221.40
Purchase #6	$38.30	9.677%	$42.0063	$42.01	$42.00	$42.00
Purchase #7	$100.85	11.440%	$112.3872	$112.39	$112.40	$112.40
7 purchase totals =	$750.47		$823.0913	$823.09	$823.05	$823.00