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	$23.50	3.489%	$24.3199	$24.32	$24.30	$24.30
Purchase #2	$117.39	12.829%	$132.45	$132.45	$132.45	$132.50
Purchase #3	$181.81	4.535%	$190.0551	$190.06	$190.05	$190.10
Purchase #4	$31.45	3.496%	$32.5495	$32.55	$32.55	$32.50
Purchase #5	$135.96	10.435%	$150.1474	$150.15	$150.15	$150.10
Purchase #6	$235.43	5.589%	$248.5882	$248.59	$248.60	$248.60
Purchase #7	$15.68	13.851%	$17.8518	$17.85	$17.85	$17.90
7 purchase totals =	$741.22		$795.9619	$795.97	$795.95	$796.00