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	$57.84	11.666%	$64.5876	$64.59	$64.60	$64.60
Purchase #2	$114.80	11.437%	$127.9297	$127.93	$127.95	$127.90
Purchase #3	$34.46	5.141%	$36.2316	$36.23	$36.25	$36.20
Purchase #4	$32.26	13.517%	$36.6206	$36.62	$36.60	$36.60
Purchase #5	$81.97	10.464%	$90.5473	$90.55	$90.55	$90.50
Purchase #6	$7.44	13.642%	$8.455	$8.46	$8.45	$8.50
Purchase #7	$143.49	9.132%	$156.5935	$156.59	$156.60	$156.60
7 purchase totals =	$472.26		$520.9653	$520.97	$521.00	$520.90