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	$98.85	11.536%	$110.2533	$110.25	$110.25	$110.30
Purchase #2	$80.89	3.167%	$83.4518	$83.45	$83.45	$83.50
Purchase #3	$79.82	13.204%	$90.3594	$90.36	$90.35	$90.40
Purchase #4	$205.87	10.750%	$228.001	$228.00	$228.00	$228.00
Purchase #5	$117.69	4.310%	$122.7624	$122.76	$122.75	$122.80
Purchase #6	$82.72	9.357%	$90.4601	$90.46	$90.45	$90.50
Purchase #7	$211.85	7.335%	$227.3892	$227.39	$227.40	$227.40
7 purchase totals =	$877.69		$952.6772	$952.67	$952.65	$952.90