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	$31.64	3.628%	$32.7879	$32.79	$32.80	$32.80
Purchase #2	$85.33	10.466%	$94.2606	$94.26	$94.25	$94.30
Purchase #3	$193.78	13.552%	$220.0411	$220.04	$220.05	$220.00
Purchase #4	$38.67	4.296%	$40.3313	$40.33	$40.35	$40.30
Purchase #5	$84.44	11.858%	$94.4529	$94.45	$94.45	$94.50
Purchase #6	$237.77	5.485%	$250.8117	$250.81	$250.80	$250.80
Purchase #7	$153.83	4.116%	$160.1616	$160.16	$160.15	$160.20
7 purchase totals =	$825.46		$892.8471	$892.84	$892.85	$892.90