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	$13.38	12.443%	$15.0449	$15.04	$15.05	$15.00
Purchase #2	$165.89	4.459%	$173.287	$173.29	$173.30	$173.30
Purchase #3	$40.90	5.295%	$43.0657	$43.07	$43.05	$43.10
Purchase #4	$95.44	7.751%	$102.8376	$102.84	$102.85	$102.80
Purchase #5	$78.81	6.170%	$83.6726	$83.67	$83.65	$83.70
Purchase #6	$163.83	9.570%	$179.5085	$179.51	$179.50	$179.50
Purchase #7	$201.64	9.632%	$221.062	$221.06	$221.05	$221.10
7 purchase totals =	$759.89		$818.4783	$818.48	$818.45	$818.50