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	$13.40	12.838%	$15.1203	$15.12	$15.10	$15.10
Purchase #2	$197.77	3.269%	$204.2351	$204.24	$204.25	$204.20
Purchase #3	$52.83	3.121%	$54.4788	$54.48	$54.50	$54.50
Purchase #4	$180.96	10.698%	$200.3191	$200.32	$200.30	$200.30
Purchase #5	$206.42	3.828%	$214.3218	$214.32	$214.30	$214.30
Purchase #6	$178.53	3.661%	$185.066	$185.07	$185.05	$185.10
Purchase #7	$219.58	13.666%	$249.5878	$249.59	$249.60	$249.60
7 purchase totals =	$1,049.49		$1,123.1289	$1,123.14	$1,123.10	$1,123.10