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	$106.70	7.429%	$114.6267	$114.63	$114.65	$114.60
Purchase #2	$113.78	6.587%	$121.2747	$121.27	$121.25	$121.30
Purchase #3	$150.34	12.385%	$168.9596	$168.96	$168.95	$169.00
Purchase #4	$24.60	13.848%	$28.0066	$28.01	$28.00	$28.00
Purchase #5	$162.83	11.126%	$180.9465	$180.95	$180.95	$180.90
Purchase #6	$150.59	13.637%	$171.126	$171.13	$171.15	$171.10
Purchase #7	$51.70	5.327%	$54.4541	$54.45	$54.45	$54.50
7 purchase totals =	$760.54		$839.3942	$839.40	$839.40	$839.40