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	$19.96	8.771%	$21.7107	$21.71	$21.70	$21.70
Purchase #2	$29.94	4.680%	$31.3412	$31.34	$31.35	$31.30
Purchase #3	$29.51	3.309%	$30.4865	$30.49	$30.50	$30.50
Purchase #4	$118.70	4.388%	$123.9086	$123.91	$123.90	$123.90
Purchase #5	$224.85	4.302%	$234.523	$234.52	$234.50	$234.50
Purchase #6	$126.34	4.753%	$132.3449	$132.34	$132.35	$132.30
Purchase #7	$87.73	5.464%	$92.5236	$92.52	$92.50	$92.50
7 purchase totals =	$637.03		$666.8385	$666.83	$666.80	$666.70