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	$16.29	12.774%	$18.3709	$18.37	$18.35	$18.40
Purchase #2	$39.90	9.229%	$43.5824	$43.58	$43.60	$43.60
Purchase #3	$125.36	4.596%	$131.1215	$131.12	$131.10	$131.10
Purchase #4	$243.43	11.516%	$271.4634	$271.46	$271.45	$271.50
Purchase #5	$198.54	10.468%	$219.3232	$219.32	$219.30	$219.30
Purchase #6	$230.38	11.686%	$257.3022	$257.30	$257.30	$257.30
Purchase #7	$71.93	4.553%	$75.205	$75.21	$75.20	$75.20
7 purchase totals =	$925.83		$1,016.3686	$1,016.36	$1,016.30	$1,016.40