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	$25.39	6.551%	$27.0533	$27.05	$27.05	$27.10
Purchase #2	$88.43	8.535%	$95.9775	$95.98	$96.00	$96.00
Purchase #3	$115.72	11.234%	$128.72	$128.72	$128.70	$128.70
Purchase #4	$34.69	11.266%	$38.5982	$38.60	$38.60	$38.60
Purchase #5	$69.32	12.704%	$78.1264	$78.13	$78.15	$78.10
Purchase #6	$15.90	8.593%	$17.2663	$17.27	$17.25	$17.30
Purchase #7	$190.85	9.446%	$208.8777	$208.88	$208.90	$208.90
7 purchase totals =	$540.30		$594.6194	$594.63	$594.65	$594.70