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	$206.78	11.398%	$230.3488	$230.35	$230.35	$230.30
Purchase #2	$51.61	9.713%	$56.6229	$56.62	$56.60	$56.60
Purchase #3	$136.85	3.253%	$141.3017	$141.30	$141.30	$141.30
Purchase #4	$116.56	9.695%	$127.8605	$127.86	$127.85	$127.90
Purchase #5	$100.46	3.677%	$104.1539	$104.15	$104.15	$104.20
Purchase #6	$139.41	12.531%	$156.8795	$156.88	$156.90	$156.90
Purchase #7	$198.60	11.409%	$221.2583	$221.26	$221.25	$221.30
7 purchase totals =	$950.27		$1,038.4256	$1,038.42	$1,038.40	$1,038.50