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	$47.78	3.255%	$49.3352	$49.34	$49.35	$49.30
Purchase #2	$228.47	7.809%	$246.3112	$246.31	$246.30	$246.30
Purchase #3	$151.47	10.194%	$166.9109	$166.91	$166.90	$166.90
Purchase #4	$136.60	7.322%	$146.6019	$146.60	$146.60	$146.60
Purchase #5	$205.79	8.429%	$223.136	$223.14	$223.15	$223.10
Purchase #6	$39.55	10.210%	$43.5881	$43.59	$43.60	$43.60
Purchase #7	$203.38	13.846%	$231.54	$231.54	$231.55	$231.50
7 purchase totals =	$1,013.04		$1,107.4233	$1,107.43	$1,107.45	$1,107.30