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	$19.87	6.520%	$21.1655	$21.17	$21.15	$21.20
Purchase #2	$211.45	12.818%	$238.5537	$238.55	$238.55	$238.60
Purchase #3	$18.41	8.461%	$19.9677	$19.97	$19.95	$20.00
Purchase #4	$46.71	10.575%	$51.6496	$51.65	$51.65	$51.60
Purchase #5	$171.93	4.548%	$179.7494	$179.75	$179.75	$179.70
Purchase #6	$132.64	8.295%	$143.6425	$143.64	$143.65	$143.60
Purchase #7	$55.61	6.409%	$59.174	$59.17	$59.15	$59.20
7 purchase totals =	$656.62		$713.9024	$713.90	$713.85	$713.90