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	$138.64	10.542%	$153.2554	$153.26	$153.25	$153.30
Purchase #2	$53.48	13.824%	$60.8731	$60.87	$60.85	$60.90
Purchase #3	$65.51	11.214%	$72.8563	$72.86	$72.85	$72.90
Purchase #4	$38.27	3.444%	$39.588	$39.59	$39.60	$39.60
Purchase #5	$53.46	13.280%	$60.5595	$60.56	$60.55	$60.60
Purchase #6	$63.34	5.212%	$66.6413	$66.64	$66.65	$66.60
Purchase #7	$178.56	5.815%	$188.9433	$188.94	$188.95	$188.90
7 purchase totals =	$591.26		$642.7169	$642.72	$642.70	$642.80