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	$38.60	3.472%	$39.9402	$39.94	$39.95	$39.90
Purchase #2	$229.46	5.692%	$242.5209	$242.52	$242.50	$242.50
Purchase #3	$209.72	5.769%	$221.8187	$221.82	$221.80	$221.80
Purchase #4	$53.86	4.851%	$56.4727	$56.47	$56.45	$56.50
Purchase #5	$51.92	11.237%	$57.7543	$57.75	$57.75	$57.80
Purchase #6	$172.41	3.752%	$178.8788	$178.88	$178.90	$178.90
Purchase #7	$29.67	9.200%	$32.3996	$32.40	$32.40	$32.40
7 purchase totals =	$785.64		$829.7852	$829.78	$829.75	$829.80