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	$82.61	8.659%	$89.7632	$89.76	$89.75	$89.80
Purchase #2	$248.47	3.730%	$257.7379	$257.74	$257.75	$257.70
Purchase #3	$95.84	4.627%	$100.2745	$100.27	$100.25	$100.30
Purchase #4	$93.93	7.725%	$101.1861	$101.19	$101.20	$101.20
Purchase #5	$114.70	6.759%	$122.4526	$122.45	$122.45	$122.50
Purchase #6	$18.86	5.629%	$19.9216	$19.92	$19.90	$19.90
Purchase #7	$85.35	4.418%	$89.1208	$89.12	$89.10	$89.10
7 purchase totals =	$739.76		$780.4567	$780.45	$780.40	$780.50