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	$161.51	13.539%	$183.3768	$183.38	$183.40	$183.40
Purchase #2	$43.71	4.642%	$45.739	$45.74	$45.75	$45.70
Purchase #3	$21.27	5.629%	$22.4673	$22.47	$22.45	$22.50
Purchase #4	$18.75	6.104%	$19.8945	$19.89	$19.90	$19.90
Purchase #5	$116.72	13.643%	$132.6441	$132.64	$132.65	$132.60
Purchase #6	$203.44	13.727%	$231.3662	$231.37	$231.35	$231.40
Purchase #7	$30.27	4.212%	$31.545	$31.55	$31.55	$31.50
7 purchase totals =	$595.67		$667.0329	$667.04	$667.05	$667.00