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	$93.83	8.868%	$102.1508	$102.15	$102.15	$102.20
Purchase #2	$141.30	12.511%	$158.978	$158.98	$159.00	$159.00
Purchase #3	$162.66	3.549%	$168.4328	$168.43	$168.45	$168.40
Purchase #4	$232.71	7.627%	$250.4588	$250.46	$250.45	$250.50
Purchase #5	$32.36	10.137%	$35.6403	$35.64	$35.65	$35.60
Purchase #6	$20.29	4.698%	$21.2432	$21.24	$21.25	$21.20
Purchase #7	$136.64	5.661%	$144.3752	$144.38	$144.40	$144.40
7 purchase totals =	$819.79		$881.2791	$881.28	$881.35	$881.30