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	$51.84	7.847%	$55.9079	$55.91	$55.90	$55.90
Purchase #2	$25.53	12.346%	$28.6819	$28.68	$28.70	$28.70
Purchase #3	$247.55	5.311%	$260.6974	$260.70	$260.70	$260.70
Purchase #4	$80.68	12.671%	$90.903	$90.90	$90.90	$90.90
Purchase #5	$100.97	4.589%	$105.6035	$105.60	$105.60	$105.60
Purchase #6	$15.82	4.445%	$16.5232	$16.52	$16.50	$16.50
Purchase #7	$67.46	5.801%	$71.3734	$71.37	$71.35	$71.40
7 purchase totals =	$589.85		$629.6903	$629.68	$629.65	$629.70