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	$117.76	9.629%	$129.0991	$129.10	$129.10	$129.10
Purchase #2	$71.52	12.809%	$80.681	$80.68	$80.70	$80.70
Purchase #3	$70.95	7.571%	$76.3216	$76.32	$76.30	$76.30
Purchase #4	$38.51	4.192%	$40.1243	$40.12	$40.10	$40.10
Purchase #5	$122.57	4.282%	$127.8184	$127.82	$127.80	$127.80
Purchase #6	$49.49	10.396%	$54.635	$54.64	$54.65	$54.60
Purchase #7	$231.41	10.256%	$255.1434	$255.14	$255.15	$255.10
7 purchase totals =	$702.21		$763.8228	$763.82	$763.80	$763.70