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	$48.99	4.381%	$51.1363	$51.14	$51.15	$51.10
Purchase #2	$125.33	10.838%	$138.9133	$138.91	$138.90	$138.90
Purchase #3	$6.56	6.704%	$6.9998	$7.00	$7.00	$7.00
Purchase #4	$171.39	10.620%	$189.5916	$189.59	$189.60	$189.60
Purchase #5	$232.95	12.606%	$262.3157	$262.32	$262.30	$262.30
Purchase #6	$145.38	9.273%	$158.8611	$158.86	$158.85	$158.90
Purchase #7	$190.32	5.460%	$200.7115	$200.71	$200.70	$200.70
7 purchase totals =	$920.92		$1,008.5293	$1,008.53	$1,008.50	$1,008.50