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	$125.44	9.680%	$137.5826	$137.58	$137.60	$137.60
Purchase #2	$43.83	3.568%	$45.3939	$45.39	$45.40	$45.40
Purchase #3	$207.81	11.179%	$231.0411	$231.04	$231.05	$231.00
Purchase #4	$54.81	12.663%	$61.7506	$61.75	$61.75	$61.80
Purchase #5	$108.45	5.456%	$114.367	$114.37	$114.35	$114.40
Purchase #6	$128.39	6.394%	$136.5993	$136.60	$136.60	$136.60
Purchase #7	$63.88	13.363%	$72.4163	$72.42	$72.40	$72.40
7 purchase totals =	$732.61		$799.1508	$799.15	$799.15	$799.20