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	$35.38	13.329%	$40.0958	$40.10	$40.10	$40.10
Purchase #2	$113.42	4.477%	$118.4978	$118.50	$118.50	$118.50
Purchase #3	$64.81	10.303%	$71.4874	$71.49	$71.50	$71.50
Purchase #4	$91.42	5.364%	$96.3238	$96.32	$96.30	$96.30
Purchase #5	$24.28	6.584%	$25.8786	$25.88	$25.90	$25.90
Purchase #6	$7.80	3.619%	$8.0823	$8.08	$8.10	$8.10
Purchase #7	$154.98	9.427%	$169.59	$169.59	$169.60	$169.60
7 purchase totals =	$492.09		$529.9557	$529.96	$530.00	$530.00