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	$225.27	13.444%	$255.5553	$255.56	$255.55	$255.60
Purchase #2	$32.47	10.443%	$35.8608	$35.86	$35.85	$35.90
Purchase #3	$240.64	6.461%	$256.1878	$256.19	$256.20	$256.20
Purchase #4	$141.28	12.112%	$158.3918	$158.39	$158.40	$158.40
Purchase #5	$121.56	7.714%	$130.9371	$130.94	$130.95	$130.90
Purchase #6	$103.90	7.523%	$111.7164	$111.72	$111.70	$111.70
Purchase #7	$46.41	9.545%	$50.8398	$50.84	$50.85	$50.80
7 purchase totals =	$911.53		$999.4890	$999.50	$999.50	$999.50