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	$122.89	13.328%	$139.2688	$139.27	$139.25	$139.30
Purchase #2	$160.27	9.119%	$174.885	$174.89	$174.90	$174.90
Purchase #3	$140.45	9.548%	$153.8602	$153.86	$153.85	$153.90
Purchase #4	$177.40	5.736%	$187.5757	$187.58	$187.60	$187.60
Purchase #5	$39.74	7.334%	$42.6545	$42.65	$42.65	$42.70
Purchase #6	$204.38	6.439%	$217.54	$217.54	$217.55	$217.50
Purchase #7	$26.90	10.784%	$29.8009	$29.80	$29.80	$29.80
7 purchase totals =	$872.03		$945.5851	$945.59	$945.60	$945.70