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	$28.53	4.485%	$29.8096	$29.81	$29.80	$29.80
Purchase #2	$77.95	10.214%	$85.9118	$85.91	$85.90	$85.90
Purchase #3	$111.83	13.858%	$127.3274	$127.33	$127.35	$127.30
Purchase #4	$148.63	5.448%	$156.7274	$156.73	$156.75	$156.70
Purchase #5	$15.73	11.751%	$17.5784	$17.58	$17.60	$17.60
Purchase #6	$145.55	12.783%	$164.1557	$164.16	$164.15	$164.20
Purchase #7	$74.33	7.531%	$79.9278	$79.93	$79.95	$79.90
7 purchase totals =	$602.55		$661.4381	$661.45	$661.50	$661.40