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	$27.30	4.360%	$28.4903	$28.49	$28.50	$28.50
Purchase #2	$43.32	6.595%	$46.177	$46.18	$46.20	$46.20
Purchase #3	$5.89	9.720%	$6.4625	$6.46	$6.45	$6.50
Purchase #4	$102.69	9.504%	$112.4497	$112.45	$112.45	$112.40
Purchase #5	$10.35	11.451%	$11.5352	$11.54	$11.55	$11.50
Purchase #6	$62.69	10.534%	$69.2938	$69.29	$69.30	$69.30
Purchase #7	$162.89	13.833%	$185.4226	$185.42	$185.40	$185.40
7 purchase totals =	$415.13		$459.8311	$459.83	$459.85	$459.80