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	$131.25	6.319%	$139.5437	$139.54	$139.55	$139.50
Purchase #2	$191.78	11.783%	$214.3774	$214.38	$214.40	$214.40
Purchase #3	$150.58	6.702%	$160.6719	$160.67	$160.65	$160.70
Purchase #4	$235.70	10.649%	$260.7997	$260.80	$260.80	$260.80
Purchase #5	$53.30	11.636%	$59.502	$59.50	$59.50	$59.50
Purchase #6	$93.51	12.834%	$105.5111	$105.51	$105.50	$105.50
Purchase #7	$190.40	4.438%	$198.85	$198.85	$198.85	$198.90
7 purchase totals =	$1,046.52		$1,139.2558	$1,139.25	$1,139.25	$1,139.30