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	$29.57	6.528%	$31.5003	$31.50	$31.50	$31.50
Purchase #2	$77.98	11.388%	$86.8604	$86.86	$86.85	$86.90
Purchase #3	$220.63	3.278%	$227.8623	$227.86	$227.85	$227.90
Purchase #4	$214.44	10.774%	$237.5438	$237.54	$237.55	$237.50
Purchase #5	$65.52	13.128%	$74.1215	$74.12	$74.10	$74.10
Purchase #6	$161.78	3.516%	$167.4682	$167.47	$167.45	$167.50
Purchase #7	$64.40	12.327%	$72.3386	$72.34	$72.35	$72.30
7 purchase totals =	$834.32		$897.6951	$897.69	$897.65	$897.70