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	$47.95	13.349%	$54.3508	$54.35	$54.35	$54.40
Purchase #2	$144.55	9.724%	$158.606	$158.61	$158.60	$158.60
Purchase #3	$196.82	10.409%	$217.307	$217.31	$217.30	$217.30
Purchase #4	$76.49	5.848%	$80.9631	$80.96	$80.95	$81.00
Purchase #5	$38.81	12.758%	$43.7614	$43.76	$43.75	$43.80
Purchase #6	$244.99	7.825%	$264.1605	$264.16	$264.15	$264.20
Purchase #7	$18.53	8.560%	$20.1162	$20.12	$20.10	$20.10
7 purchase totals =	$768.14		$839.2650	$839.27	$839.20	$839.40