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	$97.83	12.585%	$110.1419	$110.14	$110.15	$110.10
Purchase #2	$34.83	7.196%	$37.3364	$37.34	$37.35	$37.30
Purchase #3	$77.85	11.718%	$86.9725	$86.97	$86.95	$87.00
Purchase #4	$16.32	10.849%	$18.0906	$18.09	$18.10	$18.10
Purchase #5	$17.46	9.537%	$19.1252	$19.13	$19.15	$19.10
Purchase #6	$206.29	10.172%	$227.2738	$227.27	$227.25	$227.30
Purchase #7	$83.59	7.588%	$89.9328	$89.93	$89.95	$89.90
7 purchase totals =	$534.17		$588.8732	$588.87	$588.90	$588.80