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	$35.42	7.854%	$38.2019	$38.20	$38.20	$38.20
Purchase #2	$76.42	9.207%	$83.456	$83.46	$83.45	$83.50
Purchase #3	$52.95	5.181%	$55.6933	$55.69	$55.70	$55.70
Purchase #4	$81.36	10.109%	$89.5847	$89.58	$89.60	$89.60
Purchase #5	$69.32	8.387%	$75.1339	$75.13	$75.15	$75.10
Purchase #6	$19.29	11.526%	$21.5134	$21.51	$21.50	$21.50
Purchase #7	$45.81	6.836%	$48.9416	$48.94	$48.95	$48.90
7 purchase totals =	$380.57		$412.5248	$412.51	$412.55	$412.50