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	$241.98	6.258%	$257.1231	$257.12	$257.10	$257.10
Purchase #2	$176.30	11.423%	$196.4387	$196.44	$196.45	$196.40
Purchase #3	$103.41	13.213%	$117.0736	$117.07	$117.05	$117.10
Purchase #4	$194.45	3.115%	$200.5071	$200.51	$200.50	$200.50
Purchase #5	$182.52	12.540%	$205.408	$205.41	$205.40	$205.40
Purchase #6	$244.30	4.140%	$254.414	$254.41	$254.40	$254.40
Purchase #7	$35.87	12.459%	$40.339	$40.34	$40.35	$40.30
7 purchase totals =	$1,178.83		$1,271.3035	$1,271.30	$1,271.25	$1,271.20