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	$102.79	6.671%	$109.6471	$109.65	$109.65	$109.60
Purchase #2	$27.35	4.780%	$28.6573	$28.66	$28.65	$28.70
Purchase #3	$41.49	11.785%	$46.3796	$46.38	$46.40	$46.40
Purchase #4	$116.38	12.859%	$131.3453	$131.35	$131.35	$131.30
Purchase #5	$156.97	8.804%	$170.7896	$170.79	$170.80	$170.80
Purchase #6	$98.92	13.118%	$111.8963	$111.90	$111.90	$111.90
Purchase #7	$131.81	6.374%	$140.2116	$140.21	$140.20	$140.20
7 purchase totals =	$675.71		$738.9268	$738.94	$738.95	$738.90