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	$20.92	7.457%	$22.48	$22.48	$22.50	$22.50
Purchase #2	$209.94	4.646%	$219.6938	$219.69	$219.70	$219.70
Purchase #3	$68.52	12.287%	$76.9391	$76.94	$76.95	$76.90
Purchase #4	$12.65	10.128%	$13.9312	$13.93	$13.95	$13.90
Purchase #5	$65.82	3.779%	$68.3073	$68.31	$68.30	$68.30
Purchase #6	$98.39	13.268%	$111.4444	$111.44	$111.45	$111.40
Purchase #7	$222.57	13.795%	$253.2735	$253.27	$253.25	$253.30
7 purchase totals =	$698.81		$766.0693	$766.06	$766.10	$766.00