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	$36.94	9.348%	$40.3932	$40.39	$40.40	$40.40
Purchase #2	$247.64	5.327%	$260.8318	$260.83	$260.85	$260.80
Purchase #3	$139.29	11.327%	$155.0674	$155.07	$155.05	$155.10
Purchase #4	$62.90	5.400%	$66.2966	$66.30	$66.30	$66.30
Purchase #5	$34.96	11.853%	$39.1038	$39.10	$39.10	$39.10
Purchase #6	$196.69	9.415%	$215.2084	$215.21	$215.20	$215.20
Purchase #7	$223.65	8.507%	$242.6759	$242.68	$242.70	$242.70
7 purchase totals =	$942.07		$1,019.5771	$1,019.58	$1,019.60	$1,019.60