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	$244.83	4.307%	$255.3748	$255.37	$255.35	$255.40
Purchase #2	$188.38	6.703%	$201.0071	$201.01	$201.00	$201.00
Purchase #3	$80.85	6.662%	$86.2362	$86.24	$86.25	$86.20
Purchase #4	$38.61	4.552%	$40.3675	$40.37	$40.35	$40.40
Purchase #5	$48.80	9.555%	$53.4628	$53.46	$53.45	$53.50
Purchase #6	$113.93	11.622%	$127.1709	$127.17	$127.15	$127.20
Purchase #7	$64.53	4.452%	$67.4029	$67.40	$67.40	$67.40
7 purchase totals =	$779.93		$831.0222	$831.02	$830.95	$831.10