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	$162.55	12.758%	$183.2881	$183.29	$183.30	$183.30
Purchase #2	$204.85	9.339%	$223.9809	$223.98	$224.00	$224.00
Purchase #3	$182.67	3.296%	$188.6908	$188.69	$188.70	$188.70
Purchase #4	$215.31	12.351%	$241.9029	$241.90	$241.90	$241.90
Purchase #5	$82.84	8.506%	$89.8864	$89.89	$89.90	$89.90
Purchase #6	$52.84	6.134%	$56.0812	$56.08	$56.10	$56.10
Purchase #7	$12.67	10.485%	$13.9984	$14.00	$14.00	$14.00
7 purchase totals =	$913.73		$997.8287	$997.83	$997.90	$997.90