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	$180.51	12.385%	$202.8662	$202.87	$202.85	$202.90
Purchase #2	$32.75	4.783%	$34.3164	$34.32	$34.30	$34.30
Purchase #3	$242.70	11.748%	$271.2124	$271.21	$271.20	$271.20
Purchase #4	$115.83	6.521%	$123.3833	$123.38	$123.40	$123.40
Purchase #5	$95.53	5.658%	$100.9351	$100.94	$100.95	$100.90
Purchase #6	$153.94	12.492%	$173.1702	$173.17	$173.15	$173.20
Purchase #7	$99.57	9.828%	$109.3557	$109.36	$109.35	$109.40
7 purchase totals =	$920.83		$1,015.2393	$1,015.25	$1,015.20	$1,015.30