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	$184.26	8.816%	$200.5044	$200.50	$200.50	$200.50
Purchase #2	$206.58	7.473%	$222.0177	$222.02	$222.00	$222.00
Purchase #3	$46.27	12.150%	$51.8918	$51.89	$51.90	$51.90
Purchase #4	$127.39	13.666%	$144.7991	$144.80	$144.80	$144.80
Purchase #5	$111.38	3.452%	$115.2248	$115.22	$115.20	$115.20
Purchase #6	$16.84	10.447%	$18.5993	$18.60	$18.60	$18.60
Purchase #7	$226.92	4.596%	$237.3492	$237.35	$237.35	$237.30
7 purchase totals =	$919.64		$990.3863	$990.38	$990.35	$990.30