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	$21.53	13.741%	$24.4884	$24.49	$24.50	$24.50
Purchase #2	$116.63	9.339%	$127.5221	$127.52	$127.50	$127.50
Purchase #3	$212.72	12.322%	$238.9314	$238.93	$238.95	$238.90
Purchase #4	$172.64	9.435%	$188.9286	$188.93	$188.95	$188.90
Purchase #5	$191.28	5.688%	$202.16	$202.16	$202.15	$202.20
Purchase #6	$130.33	11.591%	$145.4366	$145.44	$145.45	$145.40
Purchase #7	$176.80	13.175%	$200.0934	$200.09	$200.10	$200.10
7 purchase totals =	$1,021.93		$1,127.5605	$1,127.56	$1,127.60	$1,127.50