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	$19.61	4.178%	$20.4293	$20.43	$20.45	$20.40
Purchase #2	$156.39	12.215%	$175.493	$175.49	$175.50	$175.50
Purchase #3	$92.43	7.500%	$99.3623	$99.36	$99.35	$99.40
Purchase #4	$123.60	3.644%	$128.104	$128.10	$128.10	$128.10
Purchase #5	$170.54	8.118%	$184.3844	$184.38	$184.40	$184.40
Purchase #6	$43.32	12.178%	$48.5955	$48.60	$48.60	$48.60
Purchase #7	$246.95	10.608%	$273.1465	$273.15	$273.15	$273.10
7 purchase totals =	$852.84		$929.5150	$929.51	$929.55	$929.50