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	$120.35	6.860%	$128.606	$128.61	$128.60	$128.60
Purchase #2	$27.68	7.522%	$29.7621	$29.76	$29.75	$29.80
Purchase #3	$176.39	6.504%	$187.8624	$187.86	$187.85	$187.90
Purchase #4	$128.84	7.216%	$138.1371	$138.14	$138.15	$138.10
Purchase #5	$38.71	12.615%	$43.5933	$43.59	$43.60	$43.60
Purchase #6	$49.59	11.489%	$55.2874	$55.29	$55.30	$55.30
Purchase #7	$141.33	7.284%	$151.6245	$151.62	$151.60	$151.60
7 purchase totals =	$682.89		$734.8728	$734.87	$734.85	$734.90