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	$124.45	11.221%	$138.4145	$138.41	$138.40	$138.40
Purchase #2	$52.86	10.487%	$58.4034	$58.40	$58.40	$58.40
Purchase #3	$120.41	5.789%	$127.3805	$127.38	$127.40	$127.40
Purchase #4	$134.81	9.122%	$147.1074	$147.11	$147.10	$147.10
Purchase #5	$50.88	6.716%	$54.2971	$54.30	$54.30	$54.30
Purchase #6	$40.81	6.605%	$43.5055	$43.51	$43.50	$43.50
Purchase #7	$180.51	13.194%	$204.3265	$204.33	$204.35	$204.30
7 purchase totals =	$704.73		$773.4349	$773.44	$773.45	$773.40