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	$55.58	3.383%	$57.4603	$57.46	$57.45	$57.50
Purchase #2	$143.73	10.592%	$158.9539	$158.95	$158.95	$159.00
Purchase #3	$35.69	11.284%	$39.7173	$39.72	$39.70	$39.70
Purchase #4	$150.83	9.137%	$164.6113	$164.61	$164.60	$164.60
Purchase #5	$223.58	6.715%	$238.5934	$238.59	$238.60	$238.60
Purchase #6	$172.32	8.105%	$186.2865	$186.29	$186.30	$186.30
Purchase #7	$126.70	5.296%	$133.41	$133.41	$133.40	$133.40
7 purchase totals =	$908.43		$979.0327	$979.03	$979.00	$979.10