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	$215.31	10.787%	$238.5355	$238.54	$238.55	$238.50
Purchase #2	$22.55	6.149%	$23.9366	$23.94	$23.95	$23.90
Purchase #3	$156.33	8.788%	$170.0683	$170.07	$170.05	$170.10
Purchase #4	$101.60	10.812%	$112.585	$112.59	$112.60	$112.60
Purchase #5	$169.30	12.587%	$190.6098	$190.61	$190.60	$190.60
Purchase #6	$94.96	9.679%	$104.1512	$104.15	$104.15	$104.20
Purchase #7	$171.69	4.548%	$179.4985	$179.50	$179.50	$179.50
7 purchase totals =	$931.74		$1,019.3849	$1,019.40	$1,019.40	$1,019.40