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	$242.77	5.475%	$256.0617	$256.06	$256.05	$256.10
Purchase #2	$38.68	9.328%	$42.2881	$42.29	$42.30	$42.30
Purchase #3	$218.52	7.708%	$235.3635	$235.36	$235.35	$235.40
Purchase #4	$99.78	11.499%	$111.2537	$111.25	$111.25	$111.30
Purchase #5	$211.41	11.428%	$235.5699	$235.57	$235.55	$235.60
Purchase #6	$78.72	11.602%	$87.8531	$87.85	$87.85	$87.90
Purchase #7	$126.61	12.310%	$142.1957	$142.20	$142.20	$142.20
7 purchase totals =	$1,016.49		$1,110.5857	$1,110.58	$1,110.55	$1,110.80