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	$209.83	9.276%	$229.2938	$229.29	$229.30	$229.30
Purchase #2	$81.37	11.354%	$90.6087	$90.61	$90.60	$90.60
Purchase #3	$18.34	4.608%	$19.1851	$19.19	$19.20	$19.20
Purchase #4	$231.36	6.788%	$247.0647	$247.06	$247.05	$247.10
Purchase #5	$18.51	5.856%	$19.5939	$19.59	$19.60	$19.60
Purchase #6	$18.42	11.119%	$20.4681	$20.47	$20.45	$20.50
Purchase #7	$20.62	10.558%	$22.7971	$22.80	$22.80	$22.80
7 purchase totals =	$598.45		$649.0114	$649.01	$649.00	$649.10