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	$239.34	13.551%	$271.773	$271.77	$271.75	$271.80
Purchase #2	$172.66	4.458%	$180.3572	$180.36	$180.35	$180.40
Purchase #3	$133.86	12.749%	$150.9258	$150.93	$150.95	$150.90
Purchase #4	$100.38	7.569%	$107.9778	$107.98	$108.00	$108.00
Purchase #5	$187.41	4.656%	$196.1358	$196.14	$196.15	$196.10
Purchase #6	$39.41	10.761%	$43.6509	$43.65	$43.65	$43.70
Purchase #7	$180.60	8.546%	$196.0341	$196.03	$196.05	$196.00
7 purchase totals =	$1,053.66		$1,146.8546	$1,146.86	$1,146.90	$1,146.90