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	$30.44	9.710%	$33.3957	$33.40	$33.40	$33.40
Purchase #2	$39.38	10.697%	$43.5925	$43.59	$43.60	$43.60
Purchase #3	$31.31	5.325%	$32.9773	$32.98	$33.00	$33.00
Purchase #4	$166.50	11.565%	$185.7557	$185.76	$185.75	$185.80
Purchase #5	$164.56	4.469%	$171.9142	$171.91	$171.90	$171.90
Purchase #6	$211.72	8.147%	$228.9688	$228.97	$228.95	$229.00
Purchase #7	$74.70	7.736%	$80.4788	$80.48	$80.50	$80.50
7 purchase totals =	$718.61		$777.0830	$777.09	$777.10	$777.20