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	$92.78	12.399%	$104.2838	$104.28	$104.30	$104.30
Purchase #2	$116.60	9.320%	$127.4671	$127.47	$127.45	$127.50
Purchase #3	$35.96	4.793%	$37.6836	$37.68	$37.70	$37.70
Purchase #4	$143.42	13.312%	$162.5121	$162.51	$162.50	$162.50
Purchase #5	$94.84	4.654%	$99.2539	$99.25	$99.25	$99.30
Purchase #6	$46.45	7.847%	$50.0949	$50.09	$50.10	$50.10
Purchase #7	$44.94	10.550%	$49.6812	$49.68	$49.70	$49.70
7 purchase totals =	$574.99		$630.9766	$630.96	$631.00	$631.10