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	$92.31	9.592%	$101.1644	$101.16	$101.15	$101.20
Purchase #2	$57.33	5.621%	$60.5525	$60.55	$60.55	$60.60
Purchase #3	$63.34	5.525%	$66.8395	$66.84	$66.85	$66.80
Purchase #4	$112.95	4.479%	$118.009	$118.01	$118.00	$118.00
Purchase #5	$14.46	9.608%	$15.8493	$15.85	$15.85	$15.80
Purchase #6	$154.80	6.489%	$164.845	$164.85	$164.85	$164.80
Purchase #7	$53.35	12.143%	$59.8283	$59.83	$59.85	$59.80
7 purchase totals =	$548.54		$587.0880	$587.09	$587.10	$587.00