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	$208.68	7.142%	$223.5839	$223.58	$223.60	$223.60
Purchase #2	$154.60	6.137%	$164.0878	$164.09	$164.10	$164.10
Purchase #3	$141.78	10.326%	$156.4202	$156.42	$156.40	$156.40
Purchase #4	$28.79	6.318%	$30.609	$30.61	$30.60	$30.60
Purchase #5	$42.94	5.203%	$45.1742	$45.17	$45.15	$45.20
Purchase #6	$237.76	8.648%	$258.3215	$258.32	$258.30	$258.30
Purchase #7	$40.38	5.473%	$42.59	$42.59	$42.60	$42.60
7 purchase totals =	$854.93		$920.7866	$920.78	$920.75	$920.80