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	$38.41	12.392%	$43.1698	$43.17	$43.15	$43.20
Purchase #2	$17.55	12.684%	$19.776	$19.78	$19.80	$19.80
Purchase #3	$246.48	13.614%	$280.0358	$280.04	$280.05	$280.00
Purchase #4	$137.86	9.638%	$151.1469	$151.15	$151.15	$151.10
Purchase #5	$49.89	8.776%	$54.2683	$54.27	$54.25	$54.30
Purchase #6	$171.49	4.619%	$179.4111	$179.41	$179.40	$179.40
Purchase #7	$72.97	11.575%	$81.4163	$81.42	$81.40	$81.40
7 purchase totals =	$734.65		$809.2242	$809.24	$809.20	$809.20