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	$250.68	11.758%	$280.155	$280.16	$280.15	$280.20
Purchase #2	$227.66	4.857%	$238.7174	$238.72	$238.70	$238.70
Purchase #3	$121.84	5.474%	$128.5095	$128.51	$128.50	$128.50
Purchase #4	$158.92	9.440%	$173.922	$173.92	$173.90	$173.90
Purchase #5	$123.98	13.207%	$140.354	$140.35	$140.35	$140.40
Purchase #6	$6.30	4.115%	$6.5592	$6.56	$6.55	$6.60
Purchase #7	$243.83	4.246%	$254.183	$254.18	$254.20	$254.20
7 purchase totals =	$1,133.21		$1,222.4001	$1,222.40	$1,222.35	$1,222.50