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	$37.25	13.534%	$42.2914	$42.29	$42.30	$42.30
Purchase #2	$181.69	13.106%	$205.5023	$205.50	$205.50	$205.50
Purchase #3	$112.62	4.632%	$117.8366	$117.84	$117.85	$117.80
Purchase #4	$18.63	5.432%	$19.642	$19.64	$19.65	$19.60
Purchase #5	$248.25	11.808%	$277.5634	$277.56	$277.55	$277.60
Purchase #6	$40.93	3.683%	$42.4375	$42.44	$42.45	$42.40
Purchase #7	$126.96	8.121%	$137.2704	$137.27	$137.25	$137.30
7 purchase totals =	$766.33		$842.5436	$842.54	$842.55	$842.50