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	$93.55	11.583%	$104.3859	$104.39	$104.40	$104.40
Purchase #2	$62.97	7.721%	$67.8319	$67.83	$67.85	$67.80
Purchase #3	$153.93	3.534%	$159.3699	$159.37	$159.35	$159.40
Purchase #4	$146.66	6.675%	$156.4496	$156.45	$156.45	$156.40
Purchase #5	$13.91	11.783%	$15.549	$15.55	$15.55	$15.50
Purchase #6	$182.82	4.547%	$191.1328	$191.13	$191.15	$191.10
Purchase #7	$217.81	11.835%	$243.5878	$243.59	$243.60	$243.60
7 purchase totals =	$871.65		$938.3069	$938.31	$938.35	$938.20