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	$88.95	13.425%	$100.8915	$100.89	$100.90	$100.90
Purchase #2	$62.40	11.374%	$69.4974	$69.50	$69.50	$69.50
Purchase #3	$206.34	9.471%	$225.8825	$225.88	$225.90	$225.90
Purchase #4	$45.56	6.537%	$48.5383	$48.54	$48.55	$48.50
Purchase #5	$102.70	10.526%	$113.5102	$113.51	$113.50	$113.50
Purchase #6	$160.98	6.782%	$171.8977	$171.90	$171.90	$171.90
Purchase #7	$120.96	9.433%	$132.3702	$132.37	$132.35	$132.40
7 purchase totals =	$787.89		$862.5878	$862.59	$862.60	$862.60