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	$37.87	6.864%	$40.4694	$40.47	$40.45	$40.50
Purchase #2	$206.60	5.191%	$217.3246	$217.32	$217.30	$217.30
Purchase #3	$39.79	6.830%	$42.5077	$42.51	$42.50	$42.50
Purchase #4	$75.59	12.816%	$85.2776	$85.28	$85.30	$85.30
Purchase #5	$79.91	10.368%	$88.1951	$88.20	$88.20	$88.20
Purchase #6	$64.37	3.572%	$66.6693	$66.67	$66.65	$66.70
Purchase #7	$98.52	13.189%	$111.5138	$111.51	$111.50	$111.50
7 purchase totals =	$602.65		$651.9575	$651.96	$651.90	$652.00