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	$112.96	13.458%	$128.1622	$128.16	$128.15	$128.20
Purchase #2	$66.64	8.592%	$72.3657	$72.37	$72.35	$72.40
Purchase #3	$53.84	13.417%	$61.0637	$61.06	$61.05	$61.10
Purchase #4	$230.76	3.631%	$239.1389	$239.14	$239.15	$239.10
Purchase #5	$67.25	3.377%	$69.521	$69.52	$69.50	$69.50
Purchase #6	$160.33	12.429%	$180.2574	$180.26	$180.25	$180.30
Purchase #7	$24.56	13.105%	$27.7786	$27.78	$27.80	$27.80
7 purchase totals =	$716.34		$778.2875	$778.29	$778.25	$778.40