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	$147.96	13.734%	$168.2808	$168.28	$168.30	$168.30
Purchase #2	$37.58	9.125%	$41.0092	$41.01	$41.00	$41.00
Purchase #3	$94.70	13.776%	$107.7459	$107.75	$107.75	$107.70
Purchase #4	$165.43	11.282%	$184.0938	$184.09	$184.10	$184.10
Purchase #5	$117.53	5.383%	$123.8566	$123.86	$123.85	$123.90
Purchase #6	$15.32	7.872%	$16.526	$16.53	$16.55	$16.50
Purchase #7	$61.25	4.452%	$63.9769	$63.98	$64.00	$64.00
7 purchase totals =	$639.77		$705.4892	$705.50	$705.55	$705.50