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	$164.77	13.223%	$186.5575	$186.56	$186.55	$186.60
Purchase #2	$74.62	3.265%	$77.0563	$77.06	$77.05	$77.10
Purchase #3	$136.84	12.713%	$154.2365	$154.24	$154.25	$154.20
Purchase #4	$177.79	10.445%	$196.3602	$196.36	$196.35	$196.40
Purchase #5	$56.26	12.792%	$63.4568	$63.46	$63.45	$63.50
Purchase #6	$101.60	12.570%	$114.3711	$114.37	$114.35	$114.40
Purchase #7	$206.50	4.316%	$215.4125	$215.41	$215.40	$215.40
7 purchase totals =	$918.38		$1,007.4509	$1,007.46	$1,007.40	$1,007.60