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	$17.76	4.665%	$18.5885	$18.59	$18.60	$18.60
Purchase #2	$217.41	3.274%	$224.528	$224.53	$224.55	$224.50
Purchase #3	$137.48	4.391%	$143.5167	$143.52	$143.50	$143.50
Purchase #4	$6.49	8.438%	$7.0376	$7.04	$7.05	$7.00
Purchase #5	$145.29	4.156%	$151.3283	$151.33	$151.35	$151.30
Purchase #6	$155.27	6.457%	$165.2958	$165.30	$165.30	$165.30
Purchase #7	$40.50	12.837%	$45.699	$45.70	$45.70	$45.70
7 purchase totals =	$720.20		$755.9939	$756.01	$756.05	$755.90