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	$222.37	8.709%	$241.7362	$241.74	$241.75	$241.70
Purchase #2	$143.71	10.176%	$158.3339	$158.33	$158.35	$158.30
Purchase #3	$133.39	7.582%	$143.5036	$143.50	$143.50	$143.50
Purchase #4	$169.37	4.432%	$176.8765	$176.88	$176.90	$176.90
Purchase #5	$50.77	10.179%	$55.9379	$55.94	$55.95	$55.90
Purchase #6	$127.47	10.123%	$140.3738	$140.37	$140.35	$140.40
Purchase #7	$73.82	11.733%	$82.4813	$82.48	$82.50	$82.50
7 purchase totals =	$920.90		$999.2432	$999.24	$999.30	$999.20