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	$39.94	6.686%	$42.6104	$42.61	$42.60	$42.60
Purchase #2	$243.50	11.103%	$270.5358	$270.54	$270.55	$270.50
Purchase #3	$66.96	5.406%	$70.5799	$70.58	$70.60	$70.60
Purchase #4	$10.55	13.631%	$11.9881	$11.99	$12.00	$12.00
Purchase #5	$198.76	9.461%	$217.5647	$217.56	$217.55	$217.60
Purchase #6	$199.90	8.266%	$216.4237	$216.42	$216.40	$216.40
Purchase #7	$74.87	10.497%	$82.7291	$82.73	$82.75	$82.70
7 purchase totals =	$834.48		$912.4317	$912.43	$912.45	$912.40