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	$133.63	4.560%	$139.7235	$139.72	$139.70	$139.70
Purchase #2	$155.42	7.402%	$166.9242	$166.92	$166.90	$166.90
Purchase #3	$61.32	7.162%	$65.7117	$65.71	$65.70	$65.70
Purchase #4	$71.45	12.679%	$80.5091	$80.51	$80.50	$80.50
Purchase #5	$78.31	4.417%	$81.769	$81.77	$81.75	$81.80
Purchase #6	$22.81	13.396%	$25.8656	$25.87	$25.85	$25.90
Purchase #7	$126.99	9.757%	$139.3804	$139.38	$139.40	$139.40
7 purchase totals =	$649.93		$699.8835	$699.88	$699.80	$699.90