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	$138.95	8.498%	$150.758	$150.76	$150.75	$150.80
Purchase #2	$35.43	8.750%	$38.5301	$38.53	$38.55	$38.50
Purchase #3	$91.56	13.272%	$103.7118	$103.71	$103.70	$103.70
Purchase #4	$70.80	10.169%	$77.9997	$78.00	$78.00	$78.00
Purchase #5	$182.71	12.343%	$205.2619	$205.26	$205.25	$205.30
Purchase #6	$94.30	13.289%	$106.8315	$106.83	$106.85	$106.80
Purchase #7	$150.28	11.451%	$167.4886	$167.49	$167.50	$167.50
7 purchase totals =	$764.03		$850.5816	$850.58	$850.60	$850.60