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	$103.87	7.439%	$111.5969	$111.60	$111.60	$111.60
Purchase #2	$152.43	10.218%	$168.0053	$168.01	$168.00	$168.00
Purchase #3	$36.27	6.191%	$38.5155	$38.52	$38.50	$38.50
Purchase #4	$182.47	10.871%	$202.3063	$202.31	$202.30	$202.30
Purchase #5	$15.27	8.146%	$16.5139	$16.51	$16.50	$16.50
Purchase #6	$132.57	10.776%	$146.8557	$146.86	$146.85	$146.90
Purchase #7	$51.63	8.592%	$56.066	$56.07	$56.05	$56.10
7 purchase totals =	$674.51		$739.8596	$739.88	$739.80	$739.90