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	$131.88	3.756%	$136.8334	$136.83	$136.85	$136.80
Purchase #2	$47.49	7.205%	$50.9117	$50.91	$50.90	$50.90
Purchase #3	$241.63	7.564%	$259.9069	$259.91	$259.90	$259.90
Purchase #4	$89.38	12.496%	$100.5489	$100.55	$100.55	$100.50
Purchase #5	$97.26	6.789%	$103.863	$103.86	$103.85	$103.90
Purchase #6	$213.75	5.379%	$225.2476	$225.25	$225.25	$225.20
Purchase #7	$97.58	8.195%	$105.5767	$105.58	$105.60	$105.60
7 purchase totals =	$918.97		$982.8882	$982.89	$982.90	$982.80