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	$84.60	7.239%	$90.7242	$90.72	$90.70	$90.70
Purchase #2	$137.65	11.600%	$153.6174	$153.62	$153.60	$153.60
Purchase #3	$243.77	12.577%	$274.429	$274.43	$274.45	$274.40
Purchase #4	$103.34	10.277%	$113.9603	$113.96	$113.95	$114.00
Purchase #5	$171.57	8.200%	$185.6387	$185.64	$185.65	$185.60
Purchase #6	$111.73	9.491%	$122.3343	$122.33	$122.35	$122.30
Purchase #7	$68.33	5.149%	$71.8483	$71.85	$71.85	$71.80
7 purchase totals =	$920.99		$1,012.5522	$1,012.55	$1,012.55	$1,012.40