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	$90.65	11.320%	$100.9116	$100.91	$100.90	$100.90
Purchase #2	$180.80	6.455%	$192.4706	$192.47	$192.45	$192.50
Purchase #3	$92.51	13.517%	$105.0146	$105.01	$105.00	$105.00
Purchase #4	$211.60	11.631%	$236.2112	$236.21	$236.20	$236.20
Purchase #5	$205.59	3.853%	$213.5114	$213.51	$213.50	$213.50
Purchase #6	$52.25	12.784%	$58.9296	$58.93	$58.95	$58.90
Purchase #7	$18.86	12.558%	$21.2284	$21.23	$21.25	$21.20
7 purchase totals =	$852.26		$928.2774	$928.27	$928.25	$928.20