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	$83.32	7.784%	$89.8056	$89.81	$89.80	$89.80
Purchase #2	$52.99	6.812%	$56.5997	$56.60	$56.60	$56.60
Purchase #3	$40.55	5.638%	$42.8362	$42.84	$42.85	$42.80
Purchase #4	$150.65	10.355%	$166.2498	$166.25	$166.25	$166.20
Purchase #5	$106.49	12.813%	$120.1346	$120.13	$120.15	$120.10
Purchase #6	$231.85	13.734%	$263.6923	$263.69	$263.70	$263.70
Purchase #7	$14.47	3.134%	$14.9235	$14.92	$14.90	$14.90
7 purchase totals =	$680.32		$754.2417	$754.24	$754.25	$754.10