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	$18.85	6.423%	$20.0607	$20.06	$20.05	$20.10
Purchase #2	$141.48	4.162%	$147.3684	$147.37	$147.35	$147.40
Purchase #3	$46.78	7.683%	$50.3741	$50.37	$50.35	$50.40
Purchase #4	$13.29	8.546%	$14.4258	$14.43	$14.45	$14.40
Purchase #5	$96.58	9.358%	$105.618	$105.62	$105.60	$105.60
Purchase #6	$183.43	4.451%	$191.5945	$191.59	$191.60	$191.60
Purchase #7	$185.42	13.469%	$210.3942	$210.39	$210.40	$210.40
7 purchase totals =	$685.83		$739.8357	$739.83	$739.80	$739.90