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	$54.92	8.537%	$59.6085	$59.61	$59.60	$59.60
Purchase #2	$205.33	5.466%	$216.5533	$216.55	$216.55	$216.60
Purchase #3	$229.50	11.334%	$255.5115	$255.51	$255.50	$255.50
Purchase #4	$147.33	7.708%	$158.6862	$158.69	$158.70	$158.70
Purchase #5	$44.70	10.572%	$49.4257	$49.43	$49.45	$49.40
Purchase #6	$97.44	10.298%	$107.4744	$107.47	$107.45	$107.50
Purchase #7	$9.64	6.656%	$10.2816	$10.28	$10.30	$10.30
7 purchase totals =	$788.86		$857.5412	$857.54	$857.55	$857.60