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	$81.47	9.745%	$89.4093	$89.41	$89.40	$89.40
Purchase #2	$42.58	5.410%	$44.8836	$44.88	$44.90	$44.90
Purchase #3	$165.53	13.161%	$187.3154	$187.32	$187.30	$187.30
Purchase #4	$208.55	3.525%	$215.9014	$215.90	$215.90	$215.90
Purchase #5	$182.81	13.147%	$206.844	$206.84	$206.85	$206.80
Purchase #6	$75.44	3.631%	$78.1792	$78.18	$78.20	$78.20
Purchase #7	$163.30	3.531%	$169.0661	$169.07	$169.05	$169.10
7 purchase totals =	$919.68		$991.5990	$991.60	$991.60	$991.60