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	$6.46	13.249%	$7.3159	$7.32	$7.30	$7.30
Purchase #2	$118.89	12.242%	$133.4445	$133.44	$133.45	$133.40
Purchase #3	$107.29	5.381%	$113.0633	$113.06	$113.05	$113.10
Purchase #4	$50.32	6.491%	$53.5863	$53.59	$53.60	$53.60
Purchase #5	$246.65	9.401%	$269.8376	$269.84	$269.85	$269.80
Purchase #6	$9.50	6.446%	$10.1124	$10.11	$10.10	$10.10
Purchase #7	$75.81	8.873%	$82.5366	$82.54	$82.55	$82.50
7 purchase totals =	$614.92		$669.8966	$669.90	$669.90	$669.80