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	$40.44	5.164%	$42.5283	$42.53	$42.55	$42.50
Purchase #2	$147.40	11.569%	$164.4527	$164.45	$164.45	$164.50
Purchase #3	$149.73	5.849%	$158.4877	$158.49	$158.50	$158.50
Purchase #4	$88.64	10.659%	$98.0881	$98.09	$98.10	$98.10
Purchase #5	$187.77	10.376%	$207.253	$207.25	$207.25	$207.30
Purchase #6	$59.31	7.366%	$63.6788	$63.68	$63.70	$63.70
Purchase #7	$127.73	3.608%	$132.3385	$132.34	$132.35	$132.30
7 purchase totals =	$801.02		$866.8271	$866.83	$866.90	$866.90