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	$131.77	6.452%	$140.2718	$140.27	$140.25	$140.30
Purchase #2	$42.90	10.490%	$47.4002	$47.40	$47.40	$47.40
Purchase #3	$54.35	10.167%	$59.8758	$59.88	$59.90	$59.90
Purchase #4	$198.49	3.210%	$204.8615	$204.86	$204.85	$204.90
Purchase #5	$82.44	4.422%	$86.0855	$86.09	$86.10	$86.10
Purchase #6	$49.71	8.713%	$54.0412	$54.04	$54.05	$54.00
Purchase #7	$237.57	4.448%	$248.1371	$248.14	$248.15	$248.10
7 purchase totals =	$797.23		$840.6731	$840.68	$840.70	$840.70