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	$45.39	10.759%	$50.2735	$50.27	$50.25	$50.30
Purchase #2	$80.77	11.847%	$90.3388	$90.34	$90.35	$90.30
Purchase #3	$38.53	13.530%	$43.7431	$43.74	$43.75	$43.70
Purchase #4	$14.67	6.477%	$15.6202	$15.62	$15.60	$15.60
Purchase #5	$154.29	9.246%	$168.5557	$168.56	$168.55	$168.60
Purchase #6	$175.48	7.485%	$188.6147	$188.61	$188.60	$188.60
Purchase #7	$144.71	11.223%	$160.9508	$160.95	$160.95	$161.00
7 purchase totals =	$653.84		$718.0968	$718.09	$718.05	$718.10