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	$134.86	11.274%	$150.0641	$150.06	$150.05	$150.10
Purchase #2	$187.97	3.386%	$194.3347	$194.33	$194.35	$194.30
Purchase #3	$98.68	3.388%	$102.0233	$102.02	$102.00	$102.00
Purchase #4	$177.89	13.456%	$201.8269	$201.83	$201.85	$201.80
Purchase #5	$44.36	13.775%	$50.4706	$50.47	$50.45	$50.50
Purchase #6	$169.50	13.209%	$191.8893	$191.89	$191.90	$191.90
Purchase #7	$178.28	10.212%	$196.486	$196.49	$196.50	$196.50
7 purchase totals =	$991.54		$1,087.0949	$1,087.09	$1,087.10	$1,087.10