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	$26.64	8.778%	$28.9785	$28.98	$29.00	$29.00
Purchase #2	$88.44	7.289%	$94.8864	$94.89	$94.90	$94.90
Purchase #3	$142.48	9.699%	$156.2991	$156.30	$156.30	$156.30
Purchase #4	$225.99	13.410%	$256.2953	$256.30	$256.30	$256.30
Purchase #5	$132.98	8.662%	$144.4987	$144.50	$144.50	$144.50
Purchase #6	$140.83	12.698%	$158.7126	$158.71	$158.70	$158.70
Purchase #7	$80.70	11.178%	$89.7206	$89.72	$89.70	$89.70
7 purchase totals =	$838.06		$929.3912	$929.40	$929.40	$929.40