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	$54.82	13.861%	$62.4186	$62.42	$62.40	$62.40
Purchase #2	$111.48	13.818%	$126.8843	$126.88	$126.90	$126.90
Purchase #3	$171.27	11.860%	$191.5826	$191.58	$191.60	$191.60
Purchase #4	$226.47	3.350%	$234.0567	$234.06	$234.05	$234.10
Purchase #5	$23.51	9.816%	$25.8177	$25.82	$25.80	$25.80
Purchase #6	$165.51	6.824%	$176.8044	$176.80	$176.80	$176.80
Purchase #7	$37.62	3.375%	$38.8897	$38.89	$38.90	$38.90
7 purchase totals =	$790.68		$856.4540	$856.45	$856.45	$856.50