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	$25.91	13.612%	$29.4369	$29.44	$29.45	$29.40
Purchase #2	$38.58	10.622%	$42.678	$42.68	$42.70	$42.70
Purchase #3	$190.82	4.314%	$199.052	$199.05	$199.05	$199.10
Purchase #4	$51.76	4.129%	$53.8972	$53.90	$53.90	$53.90
Purchase #5	$43.39	12.710%	$48.9049	$48.90	$48.90	$48.90
Purchase #6	$38.43	13.481%	$43.6107	$43.61	$43.60	$43.60
Purchase #7	$185.92	7.870%	$200.5519	$200.55	$200.55	$200.60
7 purchase totals =	$574.81		$618.1316	$618.13	$618.15	$618.20