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	$69.30	12.359%	$77.8648	$77.86	$77.85	$77.90
Purchase #2	$113.41	6.305%	$120.5605	$120.56	$120.55	$120.60
Purchase #3	$96.90	11.465%	$108.0096	$108.01	$108.00	$108.00
Purchase #4	$140.75	12.469%	$158.3001	$158.30	$158.30	$158.30
Purchase #5	$85.51	6.243%	$90.8484	$90.85	$90.85	$90.80
Purchase #6	$145.98	5.239%	$153.6279	$153.63	$153.65	$153.60
Purchase #7	$141.38	8.449%	$153.3252	$153.33	$153.35	$153.30
7 purchase totals =	$793.23		$862.5365	$862.54	$862.55	$862.50