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	$231.78	3.791%	$240.5668	$240.57	$240.55	$240.60
Purchase #2	$109.81	12.628%	$123.6768	$123.68	$123.70	$123.70
Purchase #3	$61.92	7.192%	$66.3733	$66.37	$66.35	$66.40
Purchase #4	$93.48	10.661%	$103.4459	$103.45	$103.45	$103.40
Purchase #5	$205.33	12.532%	$231.062	$231.06	$231.05	$231.10
Purchase #6	$99.71	13.410%	$113.0811	$113.08	$113.10	$113.10
Purchase #7	$21.25	5.650%	$22.4506	$22.45	$22.45	$22.50
7 purchase totals =	$823.28		$900.6565	$900.66	$900.65	$900.80