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	$66.69	10.193%	$73.4877	$73.49	$73.50	$73.50
Purchase #2	$104.83	8.128%	$113.3506	$113.35	$113.35	$113.40
Purchase #3	$135.70	4.808%	$142.2245	$142.22	$142.20	$142.20
Purchase #4	$44.74	8.656%	$48.6127	$48.61	$48.60	$48.60
Purchase #5	$32.46	10.542%	$35.8819	$35.88	$35.90	$35.90
Purchase #6	$98.90	4.238%	$103.0914	$103.09	$103.10	$103.10
Purchase #7	$82.30	9.764%	$90.3358	$90.34	$90.35	$90.30
7 purchase totals =	$565.62		$606.9846	$606.98	$607.00	$607.00