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	$82.60	8.544%	$89.6573	$89.66	$89.65	$89.70
Purchase #2	$152.59	4.194%	$158.9896	$158.99	$159.00	$159.00
Purchase #3	$37.50	13.580%	$42.5925	$42.59	$42.60	$42.60
Purchase #4	$21.32	3.558%	$22.0786	$22.08	$22.10	$22.10
Purchase #5	$109.31	9.696%	$119.9087	$119.91	$119.90	$119.90
Purchase #6	$178.39	3.746%	$185.0725	$185.07	$185.05	$185.10
Purchase #7	$62.49	9.556%	$68.4615	$68.46	$68.45	$68.50
7 purchase totals =	$644.20		$686.7607	$686.76	$686.75	$686.90