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	$37.51	7.775%	$40.4264	$40.43	$40.45	$40.40
Purchase #2	$30.26	8.368%	$32.7922	$32.79	$32.80	$32.80
Purchase #3	$17.40	6.810%	$18.5849	$18.58	$18.60	$18.60
Purchase #4	$133.45	13.493%	$151.4564	$151.46	$151.45	$151.50
Purchase #5	$22.51	12.549%	$25.3348	$25.33	$25.35	$25.30
Purchase #6	$132.43	8.782%	$144.06	$144.06	$144.05	$144.10
Purchase #7	$220.56	13.660%	$250.6885	$250.69	$250.70	$250.70
7 purchase totals =	$594.12		$663.3432	$663.34	$663.40	$663.40