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	$82.87	7.354%	$88.9643	$88.96	$88.95	$89.00
Purchase #2	$128.94	7.815%	$139.0167	$139.02	$139.00	$139.00
Purchase #3	$21.60	3.850%	$22.4316	$22.43	$22.45	$22.40
Purchase #4	$171.27	13.498%	$194.388	$194.39	$194.40	$194.40
Purchase #5	$48.86	5.555%	$51.5742	$51.57	$51.55	$51.60
Purchase #6	$37.83	13.303%	$42.8625	$42.86	$42.85	$42.90
Purchase #7	$117.59	4.106%	$122.4182	$122.42	$122.40	$122.40
7 purchase totals =	$608.96		$661.6555	$661.65	$661.60	$661.70