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	$239.34	6.783%	$255.5744	$255.57	$255.55	$255.60
Purchase #2	$167.64	13.223%	$189.807	$189.81	$189.80	$189.80
Purchase #3	$11.91	5.607%	$12.5778	$12.58	$12.60	$12.60
Purchase #4	$55.68	8.330%	$60.3181	$60.32	$60.30	$60.30
Purchase #5	$216.37	10.425%	$238.9266	$238.93	$238.95	$238.90
Purchase #6	$137.97	12.484%	$155.1942	$155.19	$155.20	$155.20
Purchase #7	$38.43	11.586%	$42.8825	$42.88	$42.90	$42.90
7 purchase totals =	$867.34		$955.2806	$955.28	$955.30	$955.30