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	$34.73	12.213%	$38.9716	$38.97	$38.95	$39.00
Purchase #2	$197.98	13.617%	$224.9389	$224.94	$224.95	$224.90
Purchase #3	$185.78	7.860%	$200.3823	$200.38	$200.40	$200.40
Purchase #4	$105.32	5.513%	$111.1263	$111.13	$111.15	$111.10
Purchase #5	$191.65	6.106%	$203.3521	$203.35	$203.35	$203.40
Purchase #6	$235.59	10.111%	$259.4105	$259.41	$259.40	$259.40
Purchase #7	$62.32	13.623%	$70.8099	$70.81	$70.80	$70.80
7 purchase totals =	$1,013.37		$1,108.9916	$1,108.99	$1,109.00	$1,109.00