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	$220.37	13.337%	$249.7607	$249.76	$249.75	$249.80
Purchase #2	$108.60	13.642%	$123.4152	$123.42	$123.40	$123.40
Purchase #3	$192.91	11.258%	$214.6278	$214.63	$214.65	$214.60
Purchase #4	$48.90	6.446%	$52.0521	$52.05	$52.05	$52.10
Purchase #5	$138.87	4.570%	$145.2164	$145.22	$145.20	$145.20
Purchase #6	$250.51	13.212%	$283.6074	$283.61	$283.60	$283.60
Purchase #7	$42.70	7.421%	$45.8688	$45.87	$45.85	$45.90
7 purchase totals =	$1,002.86		$1,114.5484	$1,114.56	$1,114.50	$1,114.60