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	$74.52	5.822%	$78.8586	$78.86	$78.85	$78.90
Purchase #2	$35.69	9.358%	$39.0299	$39.03	$39.05	$39.00
Purchase #3	$95.89	12.570%	$107.9434	$107.94	$107.95	$107.90
Purchase #4	$73.75	8.596%	$80.0896	$80.09	$80.10	$80.10
Purchase #5	$145.44	10.494%	$160.7025	$160.70	$160.70	$160.70
Purchase #6	$188.90	4.114%	$196.6713	$196.67	$196.65	$196.70
Purchase #7	$52.67	4.798%	$55.1971	$55.20	$55.20	$55.20
7 purchase totals =	$666.86		$718.4924	$718.49	$718.50	$718.50