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	$10.53	13.124%	$11.912	$11.91	$11.90	$11.90
Purchase #2	$55.73	13.852%	$63.4497	$63.45	$63.45	$63.40
Purchase #3	$30.88	7.342%	$33.1472	$33.15	$33.15	$33.10
Purchase #4	$55.37	12.453%	$62.2652	$62.27	$62.25	$62.30
Purchase #5	$137.57	6.574%	$146.6139	$146.61	$146.60	$146.60
Purchase #6	$162.70	11.426%	$181.2901	$181.29	$181.30	$181.30
Purchase #7	$34.78	12.190%	$39.0197	$39.02	$39.00	$39.00
7 purchase totals =	$487.56		$537.6978	$537.70	$537.65	$537.60