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	$10.89	13.442%	$12.3538	$12.35	$12.35	$12.40
Purchase #2	$104.82	6.360%	$111.4866	$111.49	$111.50	$111.50
Purchase #3	$56.35	12.767%	$63.5442	$63.54	$63.55	$63.50
Purchase #4	$242.92	9.761%	$266.6314	$266.63	$266.65	$266.60
Purchase #5	$199.72	10.411%	$220.5128	$220.51	$220.50	$220.50
Purchase #6	$133.37	13.696%	$151.6364	$151.64	$151.65	$151.60
Purchase #7	$72.59	11.290%	$80.7854	$80.79	$80.80	$80.80
7 purchase totals =	$820.66		$906.9506	$906.95	$907.00	$906.90