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	$31.97	5.841%	$33.8374	$33.84	$33.85	$33.80
Purchase #2	$172.95	4.491%	$180.7172	$180.72	$180.70	$180.70
Purchase #3	$78.71	4.184%	$82.0032	$82.00	$82.00	$82.00
Purchase #4	$171.75	4.854%	$180.0867	$180.09	$180.10	$180.10
Purchase #5	$214.88	6.611%	$229.0857	$229.09	$229.10	$229.10
Purchase #6	$246.46	13.339%	$279.3353	$279.34	$279.35	$279.30
Purchase #7	$40.49	8.326%	$43.8612	$43.86	$43.85	$43.90
7 purchase totals =	$957.21		$1,028.9267	$1,028.94	$1,028.95	$1,028.90