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	$124.51	12.304%	$139.8297	$139.83	$139.85	$139.80
Purchase #2	$30.57	4.370%	$31.9059	$31.91	$31.90	$31.90
Purchase #3	$146.48	13.868%	$166.7938	$166.79	$166.80	$166.80
Purchase #4	$151.76	13.530%	$172.2931	$172.29	$172.30	$172.30
Purchase #5	$8.86	7.185%	$9.4966	$9.50	$9.50	$9.50
Purchase #6	$13.51	9.789%	$14.8325	$14.83	$14.85	$14.80
Purchase #7	$103.99	5.504%	$109.7136	$109.71	$109.70	$109.70
7 purchase totals =	$579.68		$644.8652	$644.86	$644.90	$644.80