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	$32.68	5.564%	$34.4983	$34.50	$34.50	$34.50
Purchase #2	$29.94	6.701%	$31.9463	$31.95	$31.95	$31.90
Purchase #3	$100.71	8.834%	$109.6067	$109.61	$109.60	$109.60
Purchase #4	$112.59	13.570%	$127.8685	$127.87	$127.85	$127.90
Purchase #5	$114.68	3.477%	$118.6674	$118.67	$118.65	$118.70
Purchase #6	$164.67	12.642%	$185.4876	$185.49	$185.50	$185.50
Purchase #7	$29.70	13.835%	$33.809	$33.81	$33.80	$33.80
7 purchase totals =	$584.97		$641.8838	$641.90	$641.85	$641.90