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	$32.31	5.223%	$33.9976	$34.00	$34.00	$34.00
Purchase #2	$137.56	3.716%	$142.6717	$142.67	$142.65	$142.70
Purchase #3	$27.84	8.262%	$30.1401	$30.14	$30.15	$30.10
Purchase #4	$194.78	12.291%	$218.7204	$218.72	$218.70	$218.70
Purchase #5	$146.27	8.604%	$158.8551	$158.86	$158.85	$158.90
Purchase #6	$111.42	7.132%	$119.3665	$119.37	$119.35	$119.40
Purchase #7	$153.45	12.171%	$172.1264	$172.13	$172.15	$172.10
7 purchase totals =	$803.63		$875.8778	$875.89	$875.85	$875.90