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	$15.73	12.147%	$17.6407	$17.64	$17.65	$17.60
Purchase #2	$16.34	11.256%	$18.1792	$18.18	$18.20	$18.20
Purchase #3	$108.94	3.616%	$112.8793	$112.88	$112.90	$112.90
Purchase #4	$206.99	8.772%	$225.1472	$225.15	$225.15	$225.10
Purchase #5	$112.51	13.596%	$127.8069	$127.81	$127.80	$127.80
Purchase #6	$111.31	5.797%	$117.7626	$117.76	$117.75	$117.80
Purchase #7	$43.50	10.221%	$47.9461	$47.95	$47.95	$47.90
7 purchase totals =	$615.32		$667.3620	$667.37	$667.40	$667.30