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	$38.99	3.211%	$40.242	$40.24	$40.25	$40.20
Purchase #2	$138.68	5.140%	$145.8082	$145.81	$145.80	$145.80
Purchase #3	$232.50	4.202%	$242.2697	$242.27	$242.25	$242.30
Purchase #4	$31.82	10.185%	$35.0609	$35.06	$35.05	$35.10
Purchase #5	$212.80	5.183%	$223.8294	$223.83	$223.85	$223.80
Purchase #6	$218.68	3.839%	$227.0751	$227.08	$227.10	$227.10
Purchase #7	$160.39	7.652%	$172.663	$172.66	$172.65	$172.70
7 purchase totals =	$1,033.86		$1,086.9483	$1,086.95	$1,086.95	$1,087.00