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	$126.47	12.358%	$142.0992	$142.10	$142.10	$142.10
Purchase #2	$40.67	3.479%	$42.0849	$42.08	$42.10	$42.10
Purchase #3	$213.39	4.138%	$222.2201	$222.22	$222.20	$222.20
Purchase #4	$36.87	11.256%	$41.0201	$41.02	$41.00	$41.00
Purchase #5	$178.95	4.724%	$187.4036	$187.40	$187.40	$187.40
Purchase #6	$176.94	4.199%	$184.3697	$184.37	$184.35	$184.40
Purchase #7	$36.27	5.608%	$38.304	$38.30	$38.30	$38.30
7 purchase totals =	$809.56		$857.5016	$857.49	$857.45	$857.50