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	$66.78	8.348%	$72.3548	$72.35	$72.35	$72.40
Purchase #2	$42.38	12.424%	$47.6453	$47.65	$47.65	$47.60
Purchase #3	$238.27	9.543%	$261.0081	$261.01	$261.00	$261.00
Purchase #4	$74.56	4.310%	$77.7735	$77.77	$77.75	$77.80
Purchase #5	$133.85	7.244%	$143.5461	$143.55	$143.55	$143.50
Purchase #6	$120.49	5.699%	$127.3567	$127.36	$127.35	$127.40
Purchase #7	$120.26	12.133%	$134.8511	$134.85	$134.85	$134.90
7 purchase totals =	$796.59		$864.5356	$864.54	$864.50	$864.60