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	$215.37	4.721%	$225.5376	$225.54	$225.55	$225.50
Purchase #2	$231.27	11.341%	$257.4983	$257.50	$257.50	$257.50
Purchase #3	$22.70	9.149%	$24.7768	$24.78	$24.80	$24.80
Purchase #4	$116.41	6.405%	$123.8661	$123.87	$123.85	$123.90
Purchase #5	$35.74	13.199%	$40.4573	$40.46	$40.45	$40.50
Purchase #6	$20.82	6.418%	$22.1562	$22.16	$22.15	$22.20
Purchase #7	$134.86	8.191%	$145.9064	$145.91	$145.90	$145.90
7 purchase totals =	$777.17		$840.1987	$840.22	$840.20	$840.30