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	$217.75	6.294%	$231.4552	$231.46	$231.45	$231.50
Purchase #2	$45.29	13.607%	$51.4526	$51.45	$51.45	$51.50
Purchase #3	$15.31	10.329%	$16.8914	$16.89	$16.90	$16.90
Purchase #4	$154.86	8.681%	$168.3034	$168.30	$168.30	$168.30
Purchase #5	$123.89	6.108%	$131.4572	$131.46	$131.45	$131.50
Purchase #6	$57.86	7.335%	$62.104	$62.10	$62.10	$62.10
Purchase #7	$215.25	11.685%	$240.402	$240.40	$240.40	$240.40
7 purchase totals =	$830.21		$902.0658	$902.06	$902.05	$902.20