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	$98.87	12.743%	$111.469	$111.47	$111.45	$111.50
Purchase #2	$193.48	6.189%	$205.4545	$205.45	$205.45	$205.50
Purchase #3	$170.57	7.262%	$182.9568	$182.96	$182.95	$183.00
Purchase #4	$215.89	5.564%	$227.9021	$227.90	$227.90	$227.90
Purchase #5	$28.30	8.558%	$30.7219	$30.72	$30.70	$30.70
Purchase #6	$152.30	13.549%	$172.9351	$172.94	$172.95	$172.90
Purchase #7	$27.44	10.853%	$30.4181	$30.42	$30.40	$30.40
7 purchase totals =	$886.85		$961.8575	$961.86	$961.80	$961.90