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	$202.89	10.526%	$224.2462	$224.25	$224.25	$224.20
Purchase #2	$54.36	9.623%	$59.5911	$59.59	$59.60	$59.60
Purchase #3	$250.39	6.464%	$266.5752	$266.58	$266.60	$266.60
Purchase #4	$97.96	5.224%	$103.0774	$103.08	$103.10	$103.10
Purchase #5	$184.74	6.176%	$196.1495	$196.15	$196.15	$196.10
Purchase #6	$78.87	7.404%	$84.7095	$84.71	$84.70	$84.70
Purchase #7	$120.43	8.797%	$131.0242	$131.02	$131.00	$131.00
7 purchase totals =	$989.64		$1,065.3731	$1,065.38	$1,065.40	$1,065.30