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	$18.96	8.197%	$20.5142	$20.51	$20.50	$20.50
Purchase #2	$247.88	5.403%	$261.273	$261.27	$261.25	$261.30
Purchase #3	$239.78	6.374%	$255.0636	$255.06	$255.05	$255.10
Purchase #4	$69.75	13.628%	$79.2555	$79.26	$79.25	$79.30
Purchase #5	$226.55	12.624%	$255.1497	$255.15	$255.15	$255.10
Purchase #6	$71.60	10.232%	$78.9261	$78.93	$78.95	$78.90
Purchase #7	$170.43	6.389%	$181.3188	$181.32	$181.30	$181.30
7 purchase totals =	$1,044.95		$1,131.5009	$1,131.50	$1,131.45	$1,131.50