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	$29.73	5.809%	$31.457	$31.46	$31.45	$31.50
Purchase #2	$182.72	12.161%	$204.9406	$204.94	$204.95	$204.90
Purchase #3	$13.57	10.768%	$15.0312	$15.03	$15.05	$15.00
Purchase #4	$56.83	5.701%	$60.0699	$60.07	$60.05	$60.10
Purchase #5	$227.56	10.397%	$251.2194	$251.22	$251.20	$251.20
Purchase #6	$144.39	5.699%	$152.6188	$152.62	$152.60	$152.60
Purchase #7	$94.75	11.107%	$105.2739	$105.27	$105.25	$105.30
7 purchase totals =	$749.55		$820.6108	$820.61	$820.55	$820.60