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	$226.38	13.452%	$256.8326	$256.83	$256.85	$256.80
Purchase #2	$104.99	6.547%	$111.8637	$111.86	$111.85	$111.90
Purchase #3	$195.30	10.131%	$215.0858	$215.09	$215.10	$215.10
Purchase #4	$36.72	9.637%	$40.2587	$40.26	$40.25	$40.30
Purchase #5	$135.51	5.545%	$143.024	$143.02	$143.00	$143.00
Purchase #6	$236.63	7.693%	$254.8339	$254.83	$254.85	$254.80
Purchase #7	$13.25	12.276%	$14.8766	$14.88	$14.90	$14.90
7 purchase totals =	$948.78		$1,036.7753	$1,036.77	$1,036.80	$1,036.80