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	$20.51	10.704%	$22.7054	$22.71	$22.70	$22.70
Purchase #2	$221.49	6.594%	$236.0951	$236.10	$236.10	$236.10
Purchase #3	$201.89	6.646%	$215.3076	$215.31	$215.30	$215.30
Purchase #4	$32.34	3.567%	$33.4936	$33.49	$33.50	$33.50
Purchase #5	$245.32	4.607%	$256.6219	$256.62	$256.60	$256.60
Purchase #6	$91.37	9.548%	$100.094	$100.09	$100.10	$100.10
Purchase #7	$57.48	8.241%	$62.2169	$62.22	$62.20	$62.20
7 purchase totals =	$870.40		$926.5345	$926.54	$926.50	$926.50