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	$132.58	8.486%	$143.8307	$143.83	$143.85	$143.80
Purchase #2	$44.37	10.833%	$49.1766	$49.18	$49.20	$49.20
Purchase #3	$137.57	3.376%	$142.2144	$142.21	$142.20	$142.20
Purchase #4	$45.79	10.464%	$50.5815	$50.58	$50.60	$50.60
Purchase #5	$35.90	12.745%	$40.4755	$40.48	$40.50	$40.50
Purchase #6	$205.49	8.288%	$222.521	$222.52	$222.50	$222.50
Purchase #7	$142.88	11.351%	$159.0983	$159.10	$159.10	$159.10
7 purchase totals =	$744.58		$807.8980	$807.90	$807.95	$807.90